[llvm] [X86][ConstraintFP] Model rounding control registers for inline asm (PR #92846)

[Phoebe Wang via llvm-commits]

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@@ -74,6 +74,71 @@ define double @foo(double %0) #0 {
     ret double %8
 }
 
+define double @bar(double %0) #0 {
+; X64-LABEL: bar:
+; X64:       # %bb.0:
+; X64-NEXT:    pushq %rax
+; X64-NEXT:    #APP
+; X64-NEXT:    ldmxcsr 0
+; X64-NEXT:    #NO_APP
+; X64-NEXT:    wait
+; X64-NEXT:    movsd {{.*#+}} xmm2 = [1.0E+0,0.0E+0]
+; X64-NEXT:    movapd %xmm2, %xmm3
+; X64-NEXT:    divsd %xmm0, %xmm3
+; X64-NEXT:    #APP
+; X64-NEXT:    ldmxcsr 0
+; X64-NEXT:    #NO_APP
+; X64-NEXT:    wait
+; X64-NEXT:    movapd %xmm2, %xmm1
+; X64-NEXT:    divsd %xmm0, %xmm1
+; X64-NEXT:    #APP
+; X64-NEXT:    ldmxcsr 0
+; X64-NEXT:    #NO_APP
+; X64-NEXT:    wait
+; X64-NEXT:    divsd %xmm0, %xmm2
+; X64-NEXT:    movapd %xmm3, %xmm0
+; X64-NEXT:    callq fma at PLT
+; X64-NEXT:    popq %rax
+; X64-NEXT:    retq
+;
+; X86-LABEL: bar:
+; X86:       # %bb.0:
+; X86-NEXT:    subl $28, %esp
+; X86-NEXT:    fldl {{[0-9]+}}(%esp)
+; X86-NEXT:    #APP
+; X86-NEXT:    fldcw 0
+; X86-NEXT:    #NO_APP
+; X86-NEXT:    fld1
+; X86-NEXT:    fld %st(0)
+; X86-NEXT:    fdiv %st(2), %st
+; X86-NEXT:    #APP
+; X86-NEXT:    fldcw 0
+; X86-NEXT:    #NO_APP
+; X86-NEXT:    fld %st(1)
+; X86-NEXT:    fdiv %st(3), %st
+; X86-NEXT:    #APP
+; X86-NEXT:    fldcw 0
+; X86-NEXT:    #NO_APP
+; X86-NEXT:    fxch %st(2)
+; X86-NEXT:    fdivp %st, %st(3)
+; X86-NEXT:    fxch %st(2)
+; X86-NEXT:    fstpl {{[0-9]+}}(%esp)
+; X86-NEXT:    fstpl {{[0-9]+}}(%esp)
+; X86-NEXT:    fstpl (%esp)
+; X86-NEXT:    wait
+; X86-NEXT:    calll fma
+; X86-NEXT:    addl $28, %esp
+; X86-NEXT:    retl
+    call void asm sideeffect "SETROUND $0", "*m,~{dirflag},~{fpsr},~{flags}"(ptr elementtype(i32) null)
+    %2 = call double @llvm.experimental.constrained.fdiv.f64(double 1.000000e+00, double %0, metadata !"round.dynamic", metadata !"fpexcept.ignore") #0
+    call void asm sideeffect "SETROUND $0", "*m,~{dirflag},~{fpsr},~{flags}"(ptr elementtype(i32) null)
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phoebewang wrote:

Besides, the clobber of RC registers only makes sence under strict FP.

https://github.com/llvm/llvm-project/pull/92846