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

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

Author: RKSimon

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,

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:

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