[PATCH] D81875: [GlobalISel] Look through extends etc in CombinerHelper::matchConstantOp
Jessica Paquette via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 15 13:46:57 PDT 2020
paquette created this revision.
paquette added reviewers: aemerson, arsenm.
Herald added subscribers: hiraditya, rovka, wdng.
Herald added a project: LLVM.
It's possible to end up with a zext or something in the way of a G_CONSTANT, even pre-legalization. This can happen with memsets.
e.g.
https://godbolt.org/z/Bjc8cw
To make sure we can catch these cases, use `getConstantVRegValWithLookThrough` instead of `mi_match`.
https://reviews.llvm.org/D81875
Files:
llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
Index: llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
===================================================================
--- llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
+++ llvm/test/CodeGen/AArch64/GlobalISel/prelegalizercombiner-trivial-arith.mir
@@ -286,4 +286,24 @@
%op:_(s32) = G_SUB %x(s32), %cst
$w0 = COPY %op(s32)
RET_ReallyLR implicit $w0
+
+...
+---
+name: look_through_zext
+tracksRegLiveness: true
+body: |
+ bb.0:
+ liveins: $x0
+ ; CHECK-LABEL: name: look_through_zext
+ ; CHECK: liveins: $x0
+ ; CHECK: %zero:_(s8) = G_CONSTANT i8 0
+ ; CHECK: %zext_zero:_(s64) = G_ZEXT %zero(s8)
+ ; CHECK: $x0 = COPY %zext_zero(s64)
+ ; CHECK: RET_ReallyLR implicit $x0
+ %zero:_(s8) = G_CONSTANT i8 0
+ %zext_zero:_(s64) = G_ZEXT %zero(s8)
+ %c:_(s64) = G_CONSTANT i64 72340172838076673
+ %mul:_(s64) = G_MUL %c, %zext_zero
+ $x0 = COPY %mul(s64)
+ RET_ReallyLR implicit $x0
...
Index: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -1612,8 +1612,9 @@
bool CombinerHelper::matchConstantOp(const MachineOperand &MOP, int64_t C) {
if (!MOP.isReg())
return false;
- int64_t Cst;
- return mi_match(MOP.getReg(), MRI, m_ICst(Cst)) && Cst == C;
+ // MIPatternMatch doesn't let us look through G_ZEXT etc.
+ auto ValAndVReg = getConstantVRegValWithLookThrough(MOP.getReg(), MRI);
+ return ValAndVReg && ValAndVReg->Value == C;
}
bool CombinerHelper::replaceSingleDefInstWithOperand(MachineInstr &MI,
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