[llvm] GlobalISel: Use MIPatternMatch to look up defs in CombinerHelper (PR #216507)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/216507

Replace direct getVRegDef uses that were followed by an opcode check with
the mi_match idiom, mirroring the artifact combiner cleanup in
2e172cd38272124da30cc913f1a372ba9ea59dcf. This handles a subset of simple
cases, others call for some nicer mi_match support.

Co-authored-by: Claude (Opus 4.8) <noreply at anthropic.com>

>From 4b6fe5644cc62921c9fe1feedba7e89106ca71cf Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Fri, 14 Aug 2026 19:34:41 +0200
Subject: [PATCH] GlobalISel: Use MIPatternMatch to look up defs in
 CombinerHelper

Replace direct getVRegDef uses that were followed by an opcode check with
the mi_match idiom, mirroring the artifact combiner cleanup in
2e172cd38272124da30cc913f1a372ba9ea59dcf. This handles a subset of simple
cases, others call for some nicer mi_match support.

Co-authored-by: Claude (Opus 4.8) <noreply at anthropic.com>
---
 llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
index 8ae2a285f7fcc..c1af9b6e71b5f 100644
--- a/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -2461,7 +2461,7 @@ bool CombinerHelper::matchCombineUnmergeUndef(
       B.buildUndef(DstReg);
     }
   };
-  return isa<GImplicitDef>(MRI.getVRegDef(SrcReg));
+  return mi_match(SrcReg, MRI, m_GImplicitDef());
 }
 
 bool CombinerHelper::matchCombineUnmergeWithDeadLanesToTrunc(
@@ -6629,8 +6629,8 @@ bool CombinerHelper::matchCombineFAddFMAFMulToFMadOrFMA(
   Register Z;
   // fold (fadd (fma x, y, (fmul u, v)), z) -> (fma x, y, (fma u, v, z))
   if (LHS.MI->getOpcode() == PreferredFusedOpcode &&
-      (MRI.getVRegDef(LHS.MI->getOperand(3).getReg())->getOpcode() ==
-       TargetOpcode::G_FMUL) &&
+      mi_match(LHS.MI->getOperand(3).getReg(), MRI,
+               m_GFMul(m_Reg(), m_Reg())) &&
       MRI.hasOneNonDBGUse(LHS.MI->getOperand(0).getReg()) &&
       MRI.hasOneNonDBGUse(LHS.MI->getOperand(3).getReg())) {
     FMA = LHS.MI;
@@ -6638,8 +6638,8 @@ bool CombinerHelper::matchCombineFAddFMAFMulToFMadOrFMA(
   }
   // fold (fadd z, (fma x, y, (fmul u, v))) -> (fma x, y, (fma u, v, z))
   else if (RHS.MI->getOpcode() == PreferredFusedOpcode &&
-           (MRI.getVRegDef(RHS.MI->getOperand(3).getReg())->getOpcode() ==
-            TargetOpcode::G_FMUL) &&
+           mi_match(RHS.MI->getOperand(3).getReg(), MRI,
+                    m_GFMul(m_Reg(), m_Reg())) &&
            MRI.hasOneNonDBGUse(RHS.MI->getOperand(0).getReg()) &&
            MRI.hasOneNonDBGUse(RHS.MI->getOperand(3).getReg())) {
     Z = LHS.Reg;