release/19.x: [Clang][CodeGen] Don't emit assumptions if current block is unreachable. (#106936) #107183
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@efriedma-quic What do you think about merging this PR to the release branch? |
llvmbot
added
clang
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@llvm/pr-subscribers-clang-codegen @llvm/pr-subscribers-clang Author: None (llvmbot) ChangesBackport c94bd96 Requested by: @dtcxzyw Full diff: https://github.com/llvm/llvm-project/pull/107183.diff 2 Files Affected:
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index aa97f685ac7a9f..2f466602d2f680 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -745,7 +745,7 @@ void CodeGenFunction::EmitAttributedStmt(const AttributedStmt &S) {
} break;
case attr::CXXAssume: {
const Expr *Assumption = cast<CXXAssumeAttr>(A)->getAssumption();
- if (getLangOpts().CXXAssumptions &&
+ if (getLangOpts().CXXAssumptions && Builder.GetInsertBlock() &&
!Assumption->HasSideEffects(getContext())) {
llvm::Value *AssumptionVal = EvaluateExprAsBool(Assumption);
Builder.CreateAssumption(AssumptionVal);
diff --git a/clang/test/SemaCXX/cxx23-assume.cpp b/clang/test/SemaCXX/cxx23-assume.cpp
index 9138501d726dd6..eeae59daea3f70 100644
--- a/clang/test/SemaCXX/cxx23-assume.cpp
+++ b/clang/test/SemaCXX/cxx23-assume.cpp
@@ -158,3 +158,12 @@ foo (int x, int y)
return x + y;
}
}
+
+// Do not crash when assumptions are unreachable.
+namespace gh106898 {
+int foo () {
+ while(1);
+ int a = 0, b = 1;
+ __attribute__((assume (a < b)));
+}
+}
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efriedma-quic
approved these changes
Sep 4, 2024
…le. (llvm#106936) Fixes llvm#106898. When emitting an infinite loop, clang codegen will delete the whole block and leave builder's current block as nullptr: https://github.com/llvm/llvm-project/blob/837ee5b46a5f7f898f0de7e46a19600b896a0a1f/clang/lib/CodeGen/CGStmt.cpp#L597-L600 Then clang will create `zext (icmp slt %a, %b)` without parent block for `a < b`. It will crash here: https://github.com/llvm/llvm-project/blob/837ee5b46a5f7f898f0de7e46a19600b896a0a1f/clang/lib/CodeGen/CGExprScalar.cpp#L416-L420 Even if we disabled this optimization, it still crashes in `Builder.CreateAssumption`: https://github.com/llvm/llvm-project/blob/837ee5b46a5f7f898f0de7e46a19600b896a0a1f/llvm/lib/IR/IRBuilder.cpp#L551-L561 This patch disables assumptions emission if current block is null. (cherry picked from commit c94bd96)
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@dtcxzyw (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR. |
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Backport c94bd96
Requested by: @dtcxzyw