[llvm] Add PreLegalizer pattern matching for degrees GL extension (PR #216506)

[via llvm-commits]

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@@ -233,6 +233,44 @@ void SPIRVCombinerHelper::applySPIRVFaceForward(MachineInstr &MI) const {
   MI.eraseFromParent();
 }
 
+/// This match is part of a combine that
+/// rewrites fmul (x,180/pi) to degrees(x)
+///   (fN (g_fmul (fN X) (fN 180/pi))) -> (fN (g_intrinsic degrees (fN X)))
+///   (vXfN (g_fmul (vXfN X) (vXfN splat(180/pi)))) ->
+///   (vXfN (g_intrinsic degrees (vXfN X)))
+/// where `fN` denotes a supported floating-point type.
+bool SPIRVCombinerHelper::matchDegrees(MachineInstr &MI,
+                                       Register &MatchInfo) const {
+  Register NonConstReg;
+  std::optional<FPValueAndVReg> ConstVal;
+
+  if (!mi_match(MI.getOperand(0).getReg(), MRI,
+                m_GFMul(m_Reg(NonConstReg), m_GFCstOrSplat(ConstVal))) &&
+      !mi_match(MI.getOperand(0).getReg(), MRI,
+                m_GFMul(m_GFCstOrSplat(ConstVal), m_Reg(NonConstReg))))
+    return false;
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albertbolt1 wrote:

    this is the MIR I see for constant 
`%4:_(s32) = G_FCONSTANT float f0x42652EE1
    %5:id(s32) = G_FMUL %0, %4`
    

    and this below is the MIR i see for splat
    
    ` %6:_(s32) = G_FCONSTANT float f0x42652EE1
    %5:_(<4 x s32>) = G_BUILD_VECTOR %6(s32), %6(s32), %6(s32), %6(s32)
    %7:id(<4 x s32>) = nnan ninf nsz arcp afn reassoc G_FMUL %0, %5`

we could have more cases here ? hence keeping it in tablegen may not be the right way was what I was thinking.

kindly help here @arsenm 

https://github.com/llvm/llvm-project/pull/216506