https://github.com/ritter-x2a created
https://github.com/llvm/llvm-project/pull/130617
If we know that the initial GEP was inbounds, and we change it to a
sequence of GEPs from the same base pointer where every offset is
non-negative, then the new GEPs are inbounds.
For SWDEV-516125.
>From e880d4330b4a2fe9b281013b128763e6d24f81dd Mon Sep 17 00:00:00 2001
From: Fabian Ritter <fabian.rit...@amd.com>
Date: Mon, 10 Mar 2025 06:55:10 -0400
Subject: [PATCH] [SeparateConstOffsetFromGEP] Preserve inbounds flag based on
ValueTracking
If we know that the initial GEP was inbounds, and we change it to a
sequence of GEPs from the same base pointer where every offset is
non-negative, then the new GEPs are inbounds.
For SWDEV-516125.
---
.../Scalar/SeparateConstOffsetFromGEP.cpp | 18 +++++++++++----
.../AMDGPU/preserve-inbounds.ll | 23 +++++++++++++++++++
.../NVPTX/split-gep-and-gvn.ll | 16 ++++++-------
.../NVPTX/split-gep.ll | 8 +++----
4 files changed, 48 insertions(+), 17 deletions(-)
diff --git a/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
b/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
index 138a71ce79cef..070afdf0752f4 100644
--- a/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
+++ b/llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp
@@ -1052,6 +1052,8 @@ bool
SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
}
}
+ bool MayRecoverInbounds = AccumulativeByteOffset >= 0 && GEP->isInBounds();
+
// Remove the constant offset in each sequential index. The resultant GEP
// computes the variadic base.
// Notice that we don't remove struct field indices here. If LowerGEP is
@@ -1079,6 +1081,8 @@ bool
SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
// and the old index if they are not used.
RecursivelyDeleteTriviallyDeadInstructions(UserChainTail);
RecursivelyDeleteTriviallyDeadInstructions(OldIdx);
+ MayRecoverInbounds =
+ MayRecoverInbounds && computeKnownBits(NewIdx,
*DL).isNonNegative();
}
}
}
@@ -1100,11 +1104,15 @@ bool
SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
// address with silently-wrapping two's complement arithmetic".
// Therefore, the final code will be a semantically equivalent.
//
- // TODO(jingyue): do some range analysis to keep as many inbounds as
- // possible. GEPs with inbounds are more friendly to alias analysis.
- // TODO(gep_nowrap): Preserve nuw at least.
- auto NewGEPFlags = GEPNoWrapFlags::none();
- GEP->setNoWrapFlags(GEPNoWrapFlags::none());
+ // If the initial GEP was inbounds and all variable indices and the
+ // accumulated offsets are non-negative, they can be added in any order and
+ // the intermediate results are in bounds. So, we can preserve the inbounds
+ // flag for both GEPs. GEPs with inbounds are more friendly to alias
analysis.
+ //
+ // TODO(gep_nowrap): Preserve nuw?
+ auto NewGEPFlags =
+ MayRecoverInbounds ? GEPNoWrapFlags::inBounds() : GEPNoWrapFlags::none();
+ GEP->setNoWrapFlags(NewGEPFlags);
// Lowers a GEP to either GEPs with a single index or arithmetic operations.
if (LowerGEP) {
diff --git
a/llvm/test/Transforms/SeparateConstOffsetFromGEP/AMDGPU/preserve-inbounds.ll
b/llvm/test/Transforms/SeparateConstOffsetFromGEP/AMDGPU/preserve-inbounds.ll
index 877de38776839..91b5bc874c154 100644
---
a/llvm/test/Transforms/SeparateConstOffsetFromGEP/AMDGPU/preserve-inbounds.ll
+++
b/llvm/test/Transforms/SeparateConstOffsetFromGEP/AMDGPU/preserve-inbounds.ll
@@ -24,3 +24,26 @@ entry:
store float %3, ptr %arrayidx.dst, align 4
ret void
}
+
+; All offsets must be positive, so inbounds can be preserved.
+define void @must_be_inbounds(ptr %dst, ptr %src, i32 %i) {
+; CHECK-LABEL: @must_be_inbounds(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[I_PROM:%.*]] = zext i32 [[I:%.*]] to i64
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr inbounds float, ptr [[SRC:%.*]],
i64 [[I_PROM]]
+; CHECK-NEXT: [[ARRAYIDX_SRC2:%.*]] = getelementptr inbounds i8, ptr
[[TMP0]], i64 4
+; CHECK-NEXT: [[TMP1:%.*]] = load float, ptr [[ARRAYIDX_SRC2]], align 4
+; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds float, ptr [[DST:%.*]],
i64 [[I_PROM]]
+; CHECK-NEXT: [[ARRAYIDX_DST4:%.*]] = getelementptr inbounds i8, ptr
[[TMP2]], i64 4
+; CHECK-NEXT: store float [[TMP1]], ptr [[ARRAYIDX_DST4]], align 4
+; CHECK-NEXT: ret void
+;
+entry:
+ %i.prom = zext i32 %i to i64
+ %idx = add nsw i64 %i.prom, 1
+ %arrayidx.src = getelementptr inbounds float, ptr %src, i64 %idx
+ %3 = load float, ptr %arrayidx.src, align 4
+ %arrayidx.dst = getelementptr inbounds float, ptr %dst, i64 %idx
+ store float %3, ptr %arrayidx.dst, align 4
+ ret void
+}
diff --git
a/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
b/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
index 9a73feb2c4b5c..4474585bf9b06 100644
--- a/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
+++ b/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll
@@ -157,19 +157,19 @@ define void @sum_of_array3(i32 %x, i32 %y, ptr nocapture
%output) {
; IR-NEXT: .preheader:
; IR-NEXT: [[TMP0:%.*]] = zext i32 [[Y]] to i64
; IR-NEXT: [[TMP1:%.*]] = zext i32 [[X]] to i64
-; IR-NEXT: [[TMP2:%.*]] = getelementptr [32 x [32 x float]], ptr
addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
+; IR-NEXT: [[TMP2:%.*]] = getelementptr inbounds [32 x [32 x float]], ptr
addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
; IR-NEXT: [[TMP3:%.*]] = addrspacecast ptr addrspace(3) [[TMP2]] to ptr
; IR-NEXT: [[TMP4:%.*]] = load float, ptr [[TMP3]], align 4
; IR-NEXT: [[TMP5:%.*]] = fadd float [[TMP4]], 0.000000e+00
-; IR-NEXT: [[TMP6:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 4
+; IR-NEXT: [[TMP6:%.*]] = getelementptr inbounds i8, ptr addrspace(3)
[[TMP2]], i64 4
; IR-NEXT: [[TMP7:%.*]] = addrspacecast ptr addrspace(3) [[TMP6]] to ptr
; IR-NEXT: [[TMP8:%.*]] = load float, ptr [[TMP7]], align 4
; IR-NEXT: [[TMP9:%.*]] = fadd float [[TMP5]], [[TMP8]]
-; IR-NEXT: [[TMP10:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64
128
+; IR-NEXT: [[TMP10:%.*]] = getelementptr inbounds i8, ptr addrspace(3)
[[TMP2]], i64 128
; IR-NEXT: [[TMP11:%.*]] = addrspacecast ptr addrspace(3) [[TMP10]] to ptr
; IR-NEXT: [[TMP12:%.*]] = load float, ptr [[TMP11]], align 4
; IR-NEXT: [[TMP13:%.*]] = fadd float [[TMP9]], [[TMP12]]
-; IR-NEXT: [[TMP14:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64
132
+; IR-NEXT: [[TMP14:%.*]] = getelementptr inbounds i8, ptr addrspace(3)
[[TMP2]], i64 132
; IR-NEXT: [[TMP15:%.*]] = addrspacecast ptr addrspace(3) [[TMP14]] to ptr
; IR-NEXT: [[TMP16:%.*]] = load float, ptr [[TMP15]], align 4
; IR-NEXT: [[TMP17:%.*]] = fadd float [[TMP13]], [[TMP16]]
@@ -224,19 +224,19 @@ define void @sum_of_array4(i32 %x, i32 %y, ptr nocapture
%output) {
; IR-NEXT: .preheader:
; IR-NEXT: [[TMP0:%.*]] = zext i32 [[Y]] to i64
; IR-NEXT: [[TMP1:%.*]] = zext i32 [[X]] to i64
-; IR-NEXT: [[TMP2:%.*]] = getelementptr [32 x [32 x float]], ptr
addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
+; IR-NEXT: [[TMP2:%.*]] = getelementptr inbounds [32 x [32 x float]], ptr
addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
; IR-NEXT: [[TMP3:%.*]] = addrspacecast ptr addrspace(3) [[TMP2]] to ptr
; IR-NEXT: [[TMP4:%.*]] = load float, ptr [[TMP3]], align 4
; IR-NEXT: [[TMP5:%.*]] = fadd float [[TMP4]], 0.000000e+00
-; IR-NEXT: [[TMP6:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 4
+; IR-NEXT: [[TMP6:%.*]] = getelementptr inbounds i8, ptr addrspace(3)
[[TMP2]], i64 4
; IR-NEXT: [[TMP7:%.*]] = addrspacecast ptr addrspace(3) [[TMP6]] to ptr
; IR-NEXT: [[TMP8:%.*]] = load float, ptr [[TMP7]], align 4
; IR-NEXT: [[TMP9:%.*]] = fadd float [[TMP5]], [[TMP8]]
-; IR-NEXT: [[TMP10:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64
128
+; IR-NEXT: [[TMP10:%.*]] = getelementptr inbounds i8, ptr addrspace(3)
[[TMP2]], i64 128
; IR-NEXT: [[TMP11:%.*]] = addrspacecast ptr addrspace(3) [[TMP10]] to ptr
; IR-NEXT: [[TMP12:%.*]] = load float, ptr [[TMP11]], align 4
; IR-NEXT: [[TMP13:%.*]] = fadd float [[TMP9]], [[TMP12]]
-; IR-NEXT: [[TMP14:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64
132
+; IR-NEXT: [[TMP14:%.*]] = getelementptr inbounds i8, ptr addrspace(3)
[[TMP2]], i64 132
; IR-NEXT: [[TMP15:%.*]] = addrspacecast ptr addrspace(3) [[TMP14]] to ptr
; IR-NEXT: [[TMP16:%.*]] = load float, ptr [[TMP15]], align 4
; IR-NEXT: [[TMP17:%.*]] = fadd float [[TMP13]], [[TMP16]]
diff --git a/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
b/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
index 77b3434f4f159..da04a6e979425 100644
--- a/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
+++ b/llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll
@@ -372,8 +372,8 @@ define ptr @trunk_explicit(ptr %ptr, i64 %idx) {
; CHECK-LABEL: define ptr @trunk_explicit(
; CHECK-SAME: ptr [[PTR:%.*]], i64 [[IDX:%.*]]) {
; CHECK-NEXT: entry:
-; CHECK-NEXT: [[TMP0:%.*]] = getelementptr [[STRUCT0:%.*]], ptr [[PTR]],
i64 0, i32 3, i64 [[IDX]], i32 1
-; CHECK-NEXT: [[PTR21:%.*]] = getelementptr i8, ptr [[TMP0]], i64 3216
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr inbounds [[STRUCT0:%.*]], ptr
[[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
+; CHECK-NEXT: [[PTR21:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64
3216
; CHECK-NEXT: ret ptr [[PTR21]]
;
entry:
@@ -389,8 +389,8 @@ define ptr @trunk_long_idx(ptr %ptr, i64 %idx) {
; CHECK-LABEL: define ptr @trunk_long_idx(
; CHECK-SAME: ptr [[PTR:%.*]], i64 [[IDX:%.*]]) {
; CHECK-NEXT: entry:
-; CHECK-NEXT: [[TMP0:%.*]] = getelementptr [[STRUCT0:%.*]], ptr [[PTR]],
i64 0, i32 3, i64 [[IDX]], i32 1
-; CHECK-NEXT: [[PTR21:%.*]] = getelementptr i8, ptr [[TMP0]], i64 3216
+; CHECK-NEXT: [[TMP0:%.*]] = getelementptr inbounds [[STRUCT0:%.*]], ptr
[[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
+; CHECK-NEXT: [[PTR21:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64
3216
; CHECK-NEXT: ret ptr [[PTR21]]
;
entry:
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