llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang
Author: Shivam Gupta (xgupta)
<details>
<summary>Changes</summary>
When a matching constraint is used with a register variable, preserve the
matching constraint instead of replacing it with a fixed-register constraint.
For example, a constraint such as "0" must remain a matching constraint even
when the corresponding register variable is assigned to a specific register.
Replacing it with "{r8}" loses the relationship between the input and output
operands.
This can result in invalid code when the matching constraint requires the input
operand to use the same register as an output operand.
Fixes: #<!-- -->44930
---
Full diff: https://github.com/llvm/llvm-project/pull/216596.diff
4 Files Affected:
- (modified) clang/docs/ReleaseNotes.md (+1)
- (modified) clang/lib/AST/Stmt.cpp (+4)
- (modified) clang/test/CodeGen/PowerPC/inline-asm-matching-constraint.c (+1-1)
- (added) clang/test/CodeGen/inline-asm-register-variable-matching.c (+19)
``````````diff
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index db065773d5285..5f6d020a94d22 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -415,6 +415,7 @@ features cannot lower the translation-unit ABI level;
- Fixed an ICE that occurred when a structured binding pack is expanded
outside the lambda where it was declared. (#GH214160)
- Fixed a bug where a stray closing curley brace in an OpenMP/OpenACC pragma
could cause pragma parsing issues when inside of a member function. (#GH214195)
- Fixed a bug where preprocessor directives following comments were not
correctly recognized when using -C. (#GH48361)
+- Fixed a bug where inline assembly matching constraints were not preserved
for register variables. (#GH44930)
#### Bug Fixes to Compiler Builtins
diff --git a/clang/lib/AST/Stmt.cpp b/clang/lib/AST/Stmt.cpp
index 15d0e6435aaf3..433eadde09693 100644
--- a/clang/lib/AST/Stmt.cpp
+++ b/clang/lib/AST/Stmt.cpp
@@ -474,6 +474,10 @@ AsmStmt::addVariableConstraints(StringRef Constraint,
const Expr &AsmExpr,
return Constraint.str();
StringRef Register = Attr->getLabel();
assert(Target.isValidGCCRegisterName(Register));
+ // Preserve matching constraints instead of replacing them with the
+ // register variable's fixed register.
+ if (Constraint[0] == '%' || isdigit(Constraint[0]))
+ return Constraint.str();
// We're using validateOutputConstraint here because we only care if
// this is a register constraint.
TargetInfo::ConstraintInfo Info(Constraint, "");
diff --git a/clang/test/CodeGen/PowerPC/inline-asm-matching-constraint.c
b/clang/test/CodeGen/PowerPC/inline-asm-matching-constraint.c
index 45c387f05ce20..62fb3da2b73ab 100644
--- a/clang/test/CodeGen/PowerPC/inline-asm-matching-constraint.c
+++ b/clang/test/CodeGen/PowerPC/inline-asm-matching-constraint.c
@@ -8,4 +8,4 @@ void a(void) {
// Check that we can generate code for this correctly. The matching input
// constraint should not have an early clobber on it.
-// CHECK: call i64 asm sideeffect "mfcr $0", "=&{r0},{r0}"
+// CHECK: call i64 asm sideeffect "mfcr $0", "=&{r0},0"
diff --git a/clang/test/CodeGen/inline-asm-register-variable-matching.c
b/clang/test/CodeGen/inline-asm-register-variable-matching.c
new file mode 100644
index 0000000000000..19a73c32d75f9
--- /dev/null
+++ b/clang/test/CodeGen/inline-asm-register-variable-matching.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple s390x-unknown-linux-gnu -emit-llvm -o - %s |
FileCheck %s
+
+void test() {
+ unsigned long sum_high = 1, sum_low = 2;
+ register unsigned long a_high asm("r8") = 3;
+ register unsigned long a_low asm("r9") = 4;
+ unsigned long b_high = 5, b_low = 6;
+
+ __asm__ (
+ "algr\t%1,%5\n\t"
+ "alcgr\t%0,%3"
+ : "=r"(sum_high), "=&r"(sum_low)
+ : "0"(a_high), "r"(b_high),
+ "%1"(a_low), "r"(b_low)
+ : "cc");
+}
+
+// CHECK-NOT: "=r,=&r,{r8},r,{r9},r,~{cc}"
+// CHECK: "=r,=&r,0,r,%1,r,~{cc}"
``````````
</details>
https://github.com/llvm/llvm-project/pull/216596
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