[llvm] [AArch64][GlobalISel] Take abs scalar codegen closer to SDAG (PR #84886)

[Madhur Amilkanthwar via llvm-commits]

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@@ -3914,8 +3914,12 @@ LegalizerHelper::lower(MachineInstr &MI, unsigned TypeIdx, LLT LowerHintTy) {
   case G_SSHLSAT:
   case G_USHLSAT:
     return lowerShlSat(MI);
-  case G_ABS:
+  case G_ABS: {
+    LLT Ty = MRI.getType(MI.getOperand(0).getReg());
+    if (LI.isLegalOrCustom({G_ABS, Ty}))
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madhur13490 wrote:

Checking for G_SELECT and G_ICMP leads to assertion when compiled for  AMDGPU in abs.ll.
`const T &llvm::ArrayRef<llvm::LLT>::operator[](size_t) const [T = llvm::LLT]: Assertion `Index < Length && "Invalid index!"' failed.`

https://github.com/llvm/llvm-project/pull/84886