[llvm] [X86][GlobalIsel] support G_FABS for f80 (PR #136718)

[Evgenii Kudriashov via llvm-commits]

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@@ -0,0 +1,52 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s  -mtriple=x86_64-unknown-linux-gnu -global-isel=0 -mattr=+x87,+sse,+sse2 -o - | FileCheck %s --check-prefix=X64
+; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu -global-isel=1 -mattr=+x87,+sse,+sse2 -o - | FileCheck %s -check-prefixes=GISEL
+
+define float @test_float_abs(float %arg) {
+; X64-LABEL: test_float_abs:
+; X64:       # %bb.0:
+; X64-NEXT:    andps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
+; X64-NEXT:    retq
+;
+; GISEL-LABEL: test_float_abs:
+; GISEL:       # %bb.0:
+; GISEL-NEXT:    movd %xmm0, %eax
+; GISEL-NEXT:    andl $2147483647, %eax # imm = 0x7FFFFFFF
+; GISEL-NEXT:    movd %eax, %xmm0
+; GISEL-NEXT:    retq
+    %abs = tail call float @llvm.fabs.f32(float %arg)
+    ret float %abs
+}
+
+define double @test_double_abs(double %arg) {
+; X64-LABEL: test_double_abs:
+; X64:       # %bb.0:
+; X64-NEXT:    andps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0
+; X64-NEXT:    retq
+;
+; GISEL-LABEL: test_double_abs:
+; GISEL:       # %bb.0:
+; GISEL-NEXT:    movabsq $9223372036854775807, %rax # imm = 0x7FFFFFFFFFFFFFFF
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e-kud wrote:

I've meant loading global variable using PLT when we need an extra load. I assume here the issue is that we can't select `andq` with the such large constant and we end up with `mov` + `and`. We can't select `andps` as SDAG. It requires to insert a value in a vector but we can't select this instruction yet because the index is of type pointer. Here was an attempt to allow matching with pointer type #111503. I'm still trying to find a good change to enable selection of vectors.

So, I'd say yes, this is expected but because of vectors, not global variables.

https://github.com/llvm/llvm-project/pull/136718