From 72d2352801d13e907ad3c4b4c746f59757c1c2b1 Mon Sep 17 00:00:00 2001 From: Philip Reames Date: Tue, 31 Aug 2021 09:17:36 -0700 Subject: [PATCH] [AlignFromAssume] Bailout w/non-constant alignments (pr51680) This is a bailout for pr51680. This pass appears to assume that the alignment operand to an align tag on an assume bundle is constant. This doesn't appear to be required anywhere, and clang happily generates non-constant alignments for cases such as this case taken from the bug report: // clang -cc1 -triple powerpc64-- -S -O1 opal_pci-min.c extern int a[]; long *b; long c; void *d(long, int *, int, long, long, long) __attribute__((__alloc_align__(6))); void e() { b = d(c, a, 0, 0, 5, c); b[0] = 0; } This was exposed by a SCEV change which allowed a non-constant alignment to reach further into the pass' code. We could generalize the pass, but for now, let's fix the crash. (cherry picked from commit 9b45fd909ffa754acbb4e927bc2d55c7ab0d4e3f) --- lib/Transforms/Scalar/AlignmentFromAssumptions.cpp | 4 ++++ test/Transforms/AlignmentFromAssumptions/simple.ll | 13 +++++++++++++ 2 files changed, 17 insertions(+) diff --git a/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp b/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp index be21db9087d..e4ec5f266eb 100644 --- a/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp +++ b/lib/Transforms/Scalar/AlignmentFromAssumptions.cpp @@ -221,6 +221,10 @@ bool AlignmentFromAssumptionsPass::extractAlignmentInfo(CallInst *I, AAPtr = AAPtr->stripPointerCastsSameRepresentation(); AlignSCEV = SE->getSCEV(AlignOB.Inputs[1].get()); AlignSCEV = SE->getTruncateOrZeroExtend(AlignSCEV, Int64Ty); + if (!isa(AlignSCEV)) + // Added to suppress a crash because consumer doesn't expect non-constant + // alignments in the assume bundle. TODO: Consider generalizing caller. + return false; if (AlignOB.Inputs.size() == 3) OffSCEV = SE->getSCEV(AlignOB.Inputs[2].get()); else diff --git a/test/Transforms/AlignmentFromAssumptions/simple.ll b/test/Transforms/AlignmentFromAssumptions/simple.ll index 80761ad3be6..d8b1c618e74 100644 --- a/test/Transforms/AlignmentFromAssumptions/simple.ll +++ b/test/Transforms/AlignmentFromAssumptions/simple.ll @@ -252,6 +252,19 @@ entry: ; CHECK: ret i32 undef } + +; Variable alignments appear to be legal, don't crash +define i32 @pr51680(i32* nocapture %a, i32 %align) nounwind uwtable readonly { +entry: + tail call void @llvm.assume(i1 true) ["align"(i32* %a, i32 %align)] + %0 = load i32, i32* %a, align 4 + ret i32 %0 + +; CHECK-LABEL: @pr51680 +; CHECK: load i32, i32* {{[^,]+}}, align 4 +; CHECK: ret i32 +} + declare void @llvm.assume(i1) nounwind declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i1) nounwind