https://llvm.org/bugs/show_bug.cgi?id=30480
Bug ID: 30480
Summary: [LoopInterchange] Calls with side effects should
prevent loop interchange.
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Loop Optimizer
Assignee: unassignedb...@nondot.org
Reporter: mcros...@codeaurora.org
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Given the below test case:
void foo(unsigned a);
unsigned A[100][100];
void interchange_w_call() {
for (int i = 0; i < 100; ++i)
for(int j = 0; j < 100; ++j) {
foo(A[j][i]);
A[j][i] = i * j;
}
}
The loop interchange pass will interchange this loop. However, the interchange
will change the order of the values passed to foo(). If foo() has side
effects, I believe this optimization is legal.
Compile with debug output:
clang loopinterchange.c -S -o /dev/null -O3 -mllvm -enable-loopinterchange
-mllvm -debug-only=loop-interchange
Calling populateWorklist on Func: interchange_w_call Loop: %for.cond1.preheader
Worklist size = 1
Processing LoopList of size = 2
Found 2 Loads and Stores to analyze
Found anti dependency between Src and Dst
Src: %0 = load i32, i32* %arrayidx6, align 4, !tbaa !1
Dst: store i32 %2, i32* %arrayidx6, align 4, !tbaa !1
Processing Inner Loop Id = 1 and OuterLoopId = 0
Checking if loops are tightly nested
Checking instructions in Loop header and Loop latch
Loops are perfectly nested
Loops are legal to interchange
Cost = -1
Calling Split Inner Loop
splitInnerLoopLatch done
Output of splitInnerLoopHeader InnerLoopHeaderSucc & InnerLoopHeader
splitInnerLoopHeader done
adjustLoopBranches called
Loops interchanged
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