From 2b19e3d5dda3dd7b81ea3f73f706b0c5c6a2cde0 Mon Sep 17 00:00:00 2001 From: Andreas Jonson Date: Tue, 4 Feb 2025 23:59:38 +0100 Subject: [PATCH] [ValueTracking] Handle assume( trunc x to i1) in ComputeKnownBits --- llvm/lib/Analysis/ValueTracking.cpp | 10 ++++++++++ llvm/test/Transforms/InstCombine/assume.ll | 3 +-- llvm/test/Transforms/InstSimplify/shr-nop.ll | 3 +-- 3 files changed, 12 insertions(+), 4 deletions(-) diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index d9c55330f8664..ff8f3b6ae3bc8 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -910,6 +910,16 @@ void llvm::computeKnownBitsFromContext(const Value *V, KnownBits &Known, Known.setAllZero(); return; } + auto *Trunc = dyn_cast(Arg); + if (Trunc && Trunc->getOperand(0) == V && + isValidAssumeForContext(I, Q.CxtI, Q.DT)) { + if (Trunc->hasNoUnsignedWrap()) { + Known = KnownBits::makeConstant(APInt(BitWidth, 1)); + return; + } + Known.One.setBit(0); + return; + } // The remaining tests are all recursive, so bail out if we hit the limit. if (Depth == MaxAnalysisRecursionDepth) diff --git a/llvm/test/Transforms/InstCombine/assume.ll b/llvm/test/Transforms/InstCombine/assume.ll index 1f8fa1716b2aa..e87a61a57ea47 100644 --- a/llvm/test/Transforms/InstCombine/assume.ll +++ b/llvm/test/Transforms/InstCombine/assume.ll @@ -1013,8 +1013,7 @@ define i1 @assume_trunc_nuw_eq_one(i8 %x) { ; CHECK-LABEL: @assume_trunc_nuw_eq_one( ; CHECK-NEXT: [[A:%.*]] = trunc nuw i8 [[X:%.*]] to i1 ; CHECK-NEXT: call void @llvm.assume(i1 [[A]]) -; CHECK-NEXT: [[Q:%.*]] = icmp eq i8 [[X]], 1 -; CHECK-NEXT: ret i1 [[Q]] +; CHECK-NEXT: ret i1 true ; %a = trunc nuw i8 %x to i1 call void @llvm.assume(i1 %a) diff --git a/llvm/test/Transforms/InstSimplify/shr-nop.ll b/llvm/test/Transforms/InstSimplify/shr-nop.ll index 4b9292aab4bb3..b18a1c6d30e74 100644 --- a/llvm/test/Transforms/InstSimplify/shr-nop.ll +++ b/llvm/test/Transforms/InstSimplify/shr-nop.ll @@ -385,8 +385,7 @@ define i8 @exact_lshr_lowbit_set_assume_trunc(i8 %x) { ; CHECK-LABEL: @exact_lshr_lowbit_set_assume_trunc( ; CHECK-NEXT: [[COND:%.*]] = trunc i8 [[X:%.*]] to i1 ; CHECK-NEXT: call void @llvm.assume(i1 [[COND]]) -; CHECK-NEXT: [[SHR:%.*]] = lshr exact i8 [[X]], 1 -; CHECK-NEXT: ret i8 [[SHR]] +; CHECK-NEXT: ret i8 [[X]] ; %cond = trunc i8 %x to i1 call void @llvm.assume(i1 %cond)