[llvm] [GlobalISel] SBFX/UBFX does not create poison (PR #165675)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-aarch64

Author: David Green (davemgreen)

<details>
<summary>Changes</summary>

This adds G_SBFX/G_UBFX to the list of instructions that do not generate poison, to allowing freeze to be hoisted above one.

---
Full diff: https://github.com/llvm/llvm-project/pull/165675.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/GlobalISel/Utils.cpp (+2) 
- (modified) llvm/test/CodeGen/AArch64/GlobalISel/combine-freeze.mir (+47) 


``````````diff
diff --git a/llvm/lib/CodeGen/GlobalISel/Utils.cpp b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
index ca82857319abc..5fab6ec506e94 100644
--- a/llvm/lib/CodeGen/GlobalISel/Utils.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/Utils.cpp
@@ -1893,6 +1893,8 @@ static bool canCreateUndefOrPoison(Register Reg, const MachineRegisterInfo &MRI,
   case TargetOpcode::G_UADDSAT:
   case TargetOpcode::G_SSUBSAT:
   case TargetOpcode::G_USUBSAT:
+  case TargetOpcode::G_SBFX:
+  case TargetOpcode::G_UBFX:
     return false;
   case TargetOpcode::G_SSHLSAT:
   case TargetOpcode::G_USHLSAT:
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/combine-freeze.mir b/llvm/test/CodeGen/AArch64/GlobalISel/combine-freeze.mir
index 6b84a8488e478..1950e602ec83a 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/combine-freeze.mir
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/combine-freeze.mir
@@ -1440,3 +1440,50 @@ body:             |
     %freeze:_(<4 x s32>) = G_FREEZE %extract
     $q0 = COPY %freeze(<4 x s32>)
     RET_ReallyLR implicit $x0
+...
+---
+name:            ubfx_does_not_generate_poison
+body:             |
+  bb.1:
+    liveins: $w0
+
+    ; CHECK-LABEL: name: ubfx_does_not_generate_poison
+    ; CHECK: liveins: $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK-NEXT: %c1:_(s64) = G_CONSTANT i64 1
+    ; CHECK-NEXT: [[FREEZE:%[0-9]+]]:_(s64) = G_FREEZE [[COPY]]
+    ; CHECK-NEXT: [[UBFX:%[0-9]+]]:_(s64) = G_UBFX [[FREEZE]], %c1(s64), %c1
+    ; CHECK-NEXT: $x0 = COPY [[UBFX]](s64)
+    ; CHECK-NEXT: RET_ReallyLR implicit $x0
+    %0:_(s64) = COPY $x0
+    %c1:_(s64) = G_CONSTANT i64 1
+    %1:_(s64) = G_UBFX %0, %c1, %c1
+    %2:_(s64) = G_FREEZE %1
+    $x0 = COPY %2(s64)
+    RET_ReallyLR implicit $x0
+
+...
+---
+name:            sbfx_does_not_generate_poison
+body:             |
+  bb.1:
+    liveins: $w0
+
+    ; CHECK-LABEL: name: sbfx_does_not_generate_poison
+    ; CHECK: liveins: $w0
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
+    ; CHECK-NEXT: %c1:_(s64) = G_CONSTANT i64 1
+    ; CHECK-NEXT: [[FREEZE:%[0-9]+]]:_(s64) = G_FREEZE [[COPY]]
+    ; CHECK-NEXT: [[SBFX:%[0-9]+]]:_(s64) = G_SBFX [[FREEZE]], %c1(s64), %c1
+    ; CHECK-NEXT: $x0 = COPY [[SBFX]](s64)
+    ; CHECK-NEXT: RET_ReallyLR implicit $x0
+    %0:_(s64) = COPY $x0
+    %c1:_(s64) = G_CONSTANT i64 1
+    %1:_(s64) = G_SBFX %0, %c1, %c1
+    %2:_(s64) = G_FREEZE %1
+    $x0 = COPY %2(s64)
+    RET_ReallyLR implicit $x0
+
+...

``````````

</details>


https://github.com/llvm/llvm-project/pull/165675