[llvm] [X86] Set x87 fld1/fldz pseudo instructions as rematerializable (PR #74592)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

<details>
<summary>Changes</summary>

No need to generate/spill/restore to cpu stack

Cleanup work to allow us to properly use isFPImmLegal and fix some regressions encountered while looking at #<!-- -->74304

---
Full diff: https://github.com/llvm/llvm-project/pull/74592.diff


3 Files Affected:

- (modified) llvm/lib/Target/X86/X86InstrFPStack.td (+1-1) 
- (modified) llvm/lib/Target/X86/X86InstrInfo.cpp (+6) 
- (modified) llvm/test/CodeGen/X86/swifterror.ll (+3-7) 


``````````diff
diff --git a/llvm/lib/Target/X86/X86InstrFPStack.td b/llvm/lib/Target/X86/X86InstrFPStack.td
index ef4c011c669ad..09655d9391211 100644
--- a/llvm/lib/Target/X86/X86InstrFPStack.td
+++ b/llvm/lib/Target/X86/X86InstrFPStack.td
@@ -524,7 +524,7 @@ def XCH_F    : FPI<0xD9, MRM1r, (outs), (ins RSTi:$op), "fxch\t$op">;
 }
 
 // Floating point constant loads.
-let SchedRW = [WriteZero], Uses = [FPCW] in {
+let SchedRW = [WriteZero], Uses = [FPCW], isReMaterializable = 1 in {
 def LD_Fp032 : FpIf32<(outs RFP32:$dst), (ins), ZeroArgFP,
                 [(set RFP32:$dst, fpimm0)]>;
 def LD_Fp132 : FpIf32<(outs RFP32:$dst), (ins), ZeroArgFP,
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index ea3bf1f101c1e..bf0845a6708b0 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -782,6 +782,12 @@ bool X86InstrInfo::isReallyTriviallyReMaterializable(
     break;
 
   case X86::LOAD_STACK_GUARD:
+  case X86::LD_Fp032:
+  case X86::LD_Fp064:
+  case X86::LD_Fp080:
+  case X86::LD_Fp132:
+  case X86::LD_Fp164:
+  case X86::LD_Fp180:
   case X86::AVX1_SETALLONES:
   case X86::AVX2_SETALLONES:
   case X86::AVX512_128_SET0:
diff --git a/llvm/test/CodeGen/X86/swifterror.ll b/llvm/test/CodeGen/X86/swifterror.ll
index 5814146a54613..8fff6405d0d89 100644
--- a/llvm/test/CodeGen/X86/swifterror.ll
+++ b/llvm/test/CodeGen/X86/swifterror.ll
@@ -243,8 +243,6 @@ define float @caller2(ptr %error_ref) {
 ; CHECK-i386-NEXT:    .cfi_offset %edi, -8
 ; CHECK-i386-NEXT:    movl 32(%esp), %esi
 ; CHECK-i386-NEXT:    leal 16(%esp), %edi
-; CHECK-i386-NEXT:    fld1
-; CHECK-i386-NEXT:    fstps {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Spill
 ; CHECK-i386-NEXT:  LBB2_1: ## %bb_loop
 ; CHECK-i386-NEXT:    ## =>This Inner Loop Header: Depth=1
 ; CHECK-i386-NEXT:    movl $0, 16(%esp)
@@ -255,7 +253,7 @@ define float @caller2(ptr %error_ref) {
 ; CHECK-i386-NEXT:    jne LBB2_4
 ; CHECK-i386-NEXT:  ## %bb.2: ## %cont
 ; CHECK-i386-NEXT:    ## in Loop: Header=BB2_1 Depth=1
-; CHECK-i386-NEXT:    flds {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Reload
+; CHECK-i386-NEXT:    fld1
 ; CHECK-i386-NEXT:    fxch %st(1)
 ; CHECK-i386-NEXT:    fucompp
 ; CHECK-i386-NEXT:    fnstsw %ax
@@ -270,7 +268,7 @@ define float @caller2(ptr %error_ref) {
 ; CHECK-i386-NEXT:    fstp %st(0)
 ; CHECK-i386-NEXT:    movl %ecx, (%esp)
 ; CHECK-i386-NEXT:    calll _free
-; CHECK-i386-NEXT:    flds {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Reload
+; CHECK-i386-NEXT:    fld1
 ; CHECK-i386-NEXT:    addl $20, %esp
 ; CHECK-i386-NEXT:    popl %esi
 ; CHECK-i386-NEXT:    popl %edi
@@ -470,8 +468,6 @@ define float @foo_loop(ptr swifterror %error_ptr_ref, i32 %cc, float %cc2) {
 ; CHECK-i386-NEXT:    fstps {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Spill
 ; CHECK-i386-NEXT:    movl 36(%esp), %esi
 ; CHECK-i386-NEXT:    movl 32(%esp), %edi
-; CHECK-i386-NEXT:    fld1
-; CHECK-i386-NEXT:    fstps {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Spill
 ; CHECK-i386-NEXT:  LBB4_1: ## %bb_loop
 ; CHECK-i386-NEXT:    ## =>This Inner Loop Header: Depth=1
 ; CHECK-i386-NEXT:    testl %esi, %esi
@@ -486,7 +482,7 @@ define float @foo_loop(ptr swifterror %error_ptr_ref, i32 %cc, float %cc2) {
 ; CHECK-i386-NEXT:  LBB4_3: ## %bb_cont
 ; CHECK-i386-NEXT:    ## in Loop: Header=BB4_1 Depth=1
 ; CHECK-i386-NEXT:    flds {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Reload
-; CHECK-i386-NEXT:    flds {{[-0-9]+}}(%e{{[sb]}}p) ## 4-byte Folded Reload
+; CHECK-i386-NEXT:    fld1
 ; CHECK-i386-NEXT:    fxch %st(1)
 ; CHECK-i386-NEXT:    fucompp
 ; CHECK-i386-NEXT:    fnstsw %ax

``````````

</details>


https://github.com/llvm/llvm-project/pull/74592