diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp --- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp +++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp @@ -1534,8 +1534,28 @@ if (!I2) return false; - // Check for physical registers on the instructions first to avoid cases like - // this: + // If we have an instruction which loads or stores, we can't guarantee that + // it is identical. + // + // For example, we may have + // + // %x1 = G_LOAD %addr (load N from @somewhere) + // ... + // call @foo + // ... + // %x2 = G_LOAD %addr (load N from @somewhere) + // ... + // %or = G_OR %x1, %x2 + // + // It's possible that @foo will modify whatever lives at the address we're + // loading from. To be safe, let's just assume that all loads and stores + // are different (unless we have something which is guaranteed to not + // change.) + if (I1->mayLoadOrStore() && !I1->isDereferenceableInvariantLoad(nullptr)) + return false; + + // Check for physical registers on the instructions first to avoid cases + // like this: // // %a = COPY $physreg // ... diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-not-really-equiv-insts.mir b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-not-really-equiv-insts.mir new file mode 100644 --- /dev/null +++ b/llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-not-really-equiv-insts.mir @@ -0,0 +1,82 @@ +# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py +# RUN: llc -mtriple aarch64 -run-pass=aarch64-prelegalizer-combiner -verify-machineinstrs %s -o - | FileCheck %s + +--- | + @g = external hidden unnamed_addr global i32, align 4 + define void @not_necessarily_equiv_loads() { ret void } + define void @invariant_loads() { ret void } + define void @both_have_to_be_invariant() { ret void } +... +--- +name: not_necessarily_equiv_loads +tracksRegLiveness: true +machineFunctionInfo: {} +body: | + bb.0: + + ; %load1 || %load2 == %load1 is not necessarily true, even though they + ; both load from the same address. Whatever is in that address may be + ; changed by another instruction which appears between them. + ; + ; Check that we don't remove the G_OR. + + ; CHECK-LABEL: name: not_necessarily_equiv_loads + ; CHECK: %ptr:_(p0) = G_GLOBAL_VALUE @g + ; CHECK: %load1:_(s32) = G_LOAD %ptr(p0) :: (load 4 from @g) + ; CHECK: %load2:_(s32) = G_LOAD %ptr(p0) :: (load 4 from @g) + ; CHECK: %or:_(s32) = G_OR %load2, %load1 + ; CHECK: G_STORE %or(s32), %ptr(p0) :: (store 4 into @g) + ; CHECK: RET_ReallyLR + %ptr:_(p0) = G_GLOBAL_VALUE @g + %load1:_(s32) = G_LOAD %ptr(p0) :: (load 4 from @g) + %load2:_(s32) = G_LOAD %ptr(p0) :: (load 4 from @g) + %or:_(s32) = G_OR %load2, %load1 + G_STORE %or(s32), %ptr(p0) :: (store 4 into @g) + RET_ReallyLR + +... +--- +name: invariant_loads +tracksRegLiveness: true +machineFunctionInfo: {} +body: | + bb.0: + + ; %load1 || %load2 == %load1 is fine here, because the loads are invariant. + + ; CHECK-LABEL: name: invariant_loads + ; CHECK: %ptr:_(p0) = G_GLOBAL_VALUE @g + ; CHECK: %load2:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable invariant load 4 from @g) + ; CHECK: G_STORE %load2(s32), %ptr(p0) :: (store 4 into @g) + ; CHECK: RET_ReallyLR + %ptr:_(p0) = G_GLOBAL_VALUE @g + %load1:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable invariant load 4 from @g) + %load2:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable invariant load 4 from @g) + %or:_(s32) = G_OR %load2, %load1 + G_STORE %or(s32), %ptr(p0) :: (store 4 into @g) + RET_ReallyLR + +... +--- +name: both_have_to_be_invariant +tracksRegLiveness: true +machineFunctionInfo: {} +body: | + bb.0: + + ; We shouldn't combine here, because the loads both have to be invariant. + + ; CHECK-LABEL: name: both_have_to_be_invariant + ; CHECK: %ptr:_(p0) = G_GLOBAL_VALUE @g + ; CHECK: %load1:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable invariant load 4 from @g) + ; CHECK: %load2:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable load 4 from @g) + ; CHECK: %or:_(s32) = G_OR %load2, %load1 + ; CHECK: G_STORE %or(s32), %ptr(p0) :: (store 4 into @g) + ; CHECK: RET_ReallyLR + %ptr:_(p0) = G_GLOBAL_VALUE @g + %load1:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable invariant load 4 from @g) + %load2:_(s32) = G_LOAD %ptr(p0) :: (dereferenceable load 4 from @g) + %or:_(s32) = G_OR %load2, %load1 + G_STORE %or(s32), %ptr(p0) :: (store 4 into @g) + RET_ReallyLR +...