[llvm-branch-commits] [llvm] [DAGCombiner][GlobalISel] Extend allMulUsesCanBeContracted with FPEXT pattern (PR #188116)

[Matt Arsenault via llvm-branch-commits]

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@@ -6329,13 +6334,66 @@ bool CombinerHelper::allMulUsesCanBeContracted(const MachineInstr &MI) const {
     if (Opcode == TargetOpcode::G_FADD || Opcode == TargetOpcode::G_FSUB)
       continue;
 
-    // G_FNEG use - contractable if all users of the fneg are G_FSUB.
+    // FNEG --> FSUB pattern
+    // Also handles FNEG --> FPEXT --> FSUB
     if (Opcode == TargetOpcode::G_FNEG) {
       Register FNegReg = UseMI.getOperand(0).getReg();
-      for (const MachineInstr &FNegUser : MRI.use_nodbg_instructions(FNegReg)) {
-        unsigned FNegUserOp = FNegUser.getOpcode();
-        if (FNegUserOp != TargetOpcode::G_FSUB)
+      // ALL users of the FNEG must be contractable FSUBs or FPEXTs leading to
+      // FSUBs
+      for (const MachineInstr &FNegUseMI :
+           MRI.use_nodbg_instructions(FNegReg)) {
+        unsigned FNegUseOpcode = FNegUseMI.getOpcode();
+
+        if (FNegUseOpcode == TargetOpcode::G_FSUB)
+          continue;
+        if (FNegUseOpcode == TargetOpcode::G_FPEXT) {
+          // FNEG --> FPEXT --> FSUB
+          Register FNegFPExtReg = FNegUseMI.getOperand(0).getReg();
+          for (const MachineInstr &FNegFPExtUseMI :
+               MRI.use_nodbg_instructions(FNegFPExtReg)) {
+            if (FNegFPExtUseMI.getOpcode() != TargetOpcode::G_FSUB)
+              return false;
+            // FPEXT use is FSUB, check if can be folded in
+            if (!TLI.isFPExtFoldable(
+                    FNegFPExtUseMI, PreferredFusedOpcode,
+                    MRI.getType(FNegFPExtUseMI.getOperand(0).getReg()),
+                    MRI.getType(FNegReg)))
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arsenm wrote:

Won't this getType be the same as the original type? 

https://github.com/llvm/llvm-project/pull/188116