diff options
Diffstat (limited to 'llvm')
| -rw-r--r-- | llvm/lib/Analysis/ValueTracking.cpp | 21 | ||||
| -rw-r--r-- | llvm/test/Transforms/InstCombine/constant-fold-alias.ll | 40 |
2 files changed, 51 insertions, 10 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index f208bb72e2e..22f0486e8a2 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -790,6 +790,17 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, return; } + // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has + // the bits of its aliasee. + if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { + if (GA->mayBeOverridden()) { + KnownZero.clearAllBits(); KnownOne.clearAllBits(); + } else { + computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1, Q); + } + return; + } + // The address of an aligned GlobalValue has trailing zeros. if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) { unsigned Align = GV->getAlignment(); @@ -815,16 +826,6 @@ void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne, KnownOne.clearAllBits(); return; } - // A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has - // the bits of its aliasee. - if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { - if (GA->mayBeOverridden()) { - KnownZero.clearAllBits(); KnownOne.clearAllBits(); - } else { - computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, TD, Depth+1, Q); - } - return; - } if (Argument *A = dyn_cast<Argument>(V)) { unsigned Align = A->getType()->isPointerTy() ? A->getParamAlignment() : 0; diff --git a/llvm/test/Transforms/InstCombine/constant-fold-alias.ll b/llvm/test/Transforms/InstCombine/constant-fold-alias.ll new file mode 100644 index 00000000000..13da0f44524 --- /dev/null +++ b/llvm/test/Transforms/InstCombine/constant-fold-alias.ll @@ -0,0 +1,40 @@ +; RUN: opt -S < %s -instcombine | FileCheck %s + +target datalayout = "e-p1:16:16-p2:32:32-p3:64:64" + +@G1 = global i32 42, align 1 +@G2 = global i32 42 +@G3 = global [4 x i8] zeroinitializer, align 1 + +@A1 = alias bitcast (i8* getelementptr inbounds ([4 x i8]* @G3, i32 0, i32 2) to i32*) +@A2 = alias inttoptr (i64 and (i64 ptrtoint (i8* getelementptr inbounds ([4 x i8]* @G3, i32 0, i32 3) to i64), i64 -4) to i32*) + +define i64 @f1() { +; This cannot be constant folded because G1 is underaligned. +; CHECK-LABEL: @f1( +; CHECK: ret i64 and + ret i64 and (i64 ptrtoint (i32* @G1 to i64), i64 1) +} + +define i64 @f2() { +; The preferred alignment for G2 allows this one to foled to zero. +; CHECK-LABEL: @f2( +; CHECK: ret i64 0 + ret i64 and (i64 ptrtoint (i32* @G2 to i64), i64 1) +} + +define i64 @g1() { +; This cannot be constant folded because A1 aliases G3 which is underalaigned. +; CHECK-LABEL: @g1( +; CHECK: ret i64 and + ret i64 and (i64 ptrtoint (i32* @A1 to i64), i64 1) +} + +define i64 @g2() { +; While A2 also aliases G3 which is underaligned, the math of A2 forces a +; certain alignment allowing this to fold to zero. +; CHECK-LABEL: @g2( +; CHECK: ret i64 0 + ret i64 and (i64 ptrtoint (i32* @A2 to i64), i64 1) +} + |
