[llvm] [X86][GlobalIsel] G_BITCAST support (PR #144473)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Mahesh-Attarde (mahesh-attarde)

<details>
<summary>Changes</summary>

Adds support for G_BITCAST

---
Full diff: https://github.com/llvm/llvm-project/pull/144473.diff


3 Files Affected:

- (modified) llvm/lib/Target/X86/GISel/X86LegalizerInfo.cpp (+19) 
- (modified) llvm/lib/Target/X86/GISel/X86LegalizerInfo.h (+2) 
- (modified) llvm/test/CodeGen/X86/bitcast.ll (+36-3) 


``````````diff
diff --git a/llvm/lib/Target/X86/GISel/X86LegalizerInfo.cpp b/llvm/lib/Target/X86/GISel/X86LegalizerInfo.cpp
index 11dd05c584983..85e6c190c7ced 100644
--- a/llvm/lib/Target/X86/GISel/X86LegalizerInfo.cpp
+++ b/llvm/lib/Target/X86/GISel/X86LegalizerInfo.cpp
@@ -669,6 +669,8 @@ bool X86LegalizerInfo::legalizeCustom(LegalizerHelper &Helper, MachineInstr &MI,
     return legalizeSITOFP(MI, MRI, Helper);
   case TargetOpcode::G_FPTOSI:
     return legalizeFPTOSI(MI, MRI, Helper);
+  case TargetOpcode::G_BITCAST:
+    return legalizeBitcast(MI, MRI, Helper);
   }
   llvm_unreachable("expected switch to return");
 }
@@ -835,6 +837,23 @@ bool X86LegalizerInfo::legalizeNarrowingStore(MachineInstr &MI,
   return true;
 }
 
+bool X86LegalizerInfo::legalizeBitcast(MachineInstr &MI,
+                                       MachineRegisterInfo &MRI,
+                                       LegalizerHelper &Helper) const {
+  MachineIRBuilder &MIRBuilder = Helper.MIRBuilder;
+  auto [DstReg, DstTy, SrcReg, SrcTy] = MI.getFirst2RegLLTs();
+  assert(!SrcTy.isVector() && "G_BITCAST does not support vectors yet");
+  bool isCopy =
+      (SrcTy == DstTy) || (SrcTy.getSizeInBits() == DstTy.getSizeInBits());
+  if (isCopy) {
+    MIRBuilder.buildCopy(DstReg, SrcReg);
+    MI.eraseFromParent();
+    return true;
+  }
+  // For Vectors specific bitcasts
+  return Helper.lowerBitcast(MI) == LegalizerHelper::LegalizeResult::Legalized;
+}
+
 bool X86LegalizerInfo::legalizeIntrinsic(LegalizerHelper &Helper,
                                          MachineInstr &MI) const {
   return true;
diff --git a/llvm/lib/Target/X86/GISel/X86LegalizerInfo.h b/llvm/lib/Target/X86/GISel/X86LegalizerInfo.h
index 1ba82674ed4c6..eb42126d079fb 100644
--- a/llvm/lib/Target/X86/GISel/X86LegalizerInfo.h
+++ b/llvm/lib/Target/X86/GISel/X86LegalizerInfo.h
@@ -54,6 +54,8 @@ class X86LegalizerInfo : public LegalizerInfo {
 
   bool legalizeFPTOSI(MachineInstr &MI, MachineRegisterInfo &MRI,
                       LegalizerHelper &Helper) const;
+  bool legalizeBitcast(MachineInstr &MI, MachineRegisterInfo &MRI,
+                       LegalizerHelper &Helper) const;
 };
 } // namespace llvm
 #endif
diff --git a/llvm/test/CodeGen/X86/bitcast.ll b/llvm/test/CodeGen/X86/bitcast.ll
index 0866a0b1b2bd1..c9193fed0ed5c 100644
--- a/llvm/test/CodeGen/X86/bitcast.ll
+++ b/llvm/test/CodeGen/X86/bitcast.ll
@@ -1,24 +1,57 @@
-; RUN: llc < %s -mtriple=i686--
-; RUN: llc < %s -mtriple=x86_64--
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=i686-- | FileCheck %s -check-prefixes=X86
+; RUN: llc < %s -mtriple=x86_64--| FileCheck %s -check-prefixes=X64
+; RUN: llc < %s -mtriple=i686--   -global-isel -global-isel-abort=0 | FileCheck %s -check-prefixes=X86
+; RUN: llc < %s -mtriple=x86_64--  -global-isel -global-isel-abort=1 | FileCheck %s -check-prefixes=X64
 ; PR1033
 
 define i64 @test1(double %t) {
+; X64-LABEL: test1:
+; X64:       # %bb.0:
+; X64-NEXT:    movq %xmm0, %rax
+; X64-NEXT:    retq
         %u = bitcast double %t to i64           ; <i64> [#uses=1]
         ret i64 %u
 }
 
 define double @test2(i64 %t) {
+; X86-LABEL: test2:
+; X86:       # %bb.0:
+; X86-NEXT:    fldl {{[0-9]+}}(%esp)
+; X86-NEXT:    retl
+;
+; X64-LABEL: test2:
+; X64:       # %bb.0:
+; X64-NEXT:    movq %rdi, %xmm0
+; X64-NEXT:    retq
         %u = bitcast i64 %t to double           ; <double> [#uses=1]
         ret double %u
 }
 
 define i32 @test3(float %t) {
+; X86-LABEL: test3:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: test3:
+; X64:       # %bb.0:
+; X64-NEXT:    movd %xmm0, %eax
+; X64-NEXT:    retq
         %u = bitcast float %t to i32            ; <i32> [#uses=1]
         ret i32 %u
 }
 
 define float @test4(i32 %t) {
+; X86-LABEL: test4:
+; X86:       # %bb.0:
+; X86-NEXT:    flds {{[0-9]+}}(%esp)
+; X86-NEXT:    retl
+;
+; X64-LABEL: test4:
+; X64:       # %bb.0:
+; X64-NEXT:    movd %edi, %xmm0
+; X64-NEXT:    retq
         %u = bitcast i32 %t to float            ; <float> [#uses=1]
         ret float %u
 }
-

``````````

</details>


https://github.com/llvm/llvm-project/pull/144473