commit 47aeeffc8fb45c4926128657dd15eaa87edab647
author Jessica Paquette <jpaquette@apple.com> Thu Jul 08 16:45:45 2021 -0700
committer Jessica Paquette <jpaquette@apple.com> Fri Jul 09 14:15:44 2021 -0700
tree ff0614fb38b6fe892955f1b4f7f539da40bb59dc
parent 9647a6f719ee4b1c23eea7aef368c1dcd5317949

[GlobalISel] Use GCDTy when extracting GCD ty from leftover regs in insertParts

`LegalizerHelper::insertParts` uses `extractGCDType` on registers split into
a desired type and a smaller leftover type. This is used to populate a list
of registers. Each register in the list will have the same type as returned by
`extractGCDType`.

If we have

- `ResultTy` = s792
- `PartTy` = s64
- `LeftoverTy` = s24

When we call `extractGCDType`, we'll end up with two different types appended
to the list:

Part: gcd(792, 64, 24) => s8
Leftover: gcd(792, 24, 24) => s24

When this happens, we'll hit an assert while trying to build a G_MERGE_VALUES.

This patch changes the code for the leftover type so that we reuse the GCD from
the desired type.

e.g.

Leftover: gcd(792, 8, 24) => s8

https://llvm.godbolt.org/z/137Kqxj6j

Differential Revision: https://reviews.llvm.org/D105674

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index 3fb5056..66cd53b 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -223,13 +223,9 @@
   }
 
   SmallVector<Register> GCDRegs;
-  LLT GCDTy;
-  for (Register PartReg : PartRegs)
-    GCDTy = extractGCDType(GCDRegs, ResultTy, LeftoverTy, PartReg);
-
-  for (Register PartReg : LeftoverRegs)
-    extractGCDType(GCDRegs, ResultTy, LeftoverTy, PartReg);
-
+  LLT GCDTy = getGCDType(getGCDType(ResultTy, LeftoverTy), PartTy);
+  for (auto PartReg : concat<const Register>(PartRegs, LeftoverRegs))
+    extractGCDType(GCDRegs, GCDTy, PartReg);
   LLT ResultLCMTy = buildLCMMergePieces(ResultTy, LeftoverTy, GCDTy, GCDRegs);
   buildWidenedRemergeToDst(DstReg, ResultLCMTy, GCDRegs);
 }