[GlobalISel] Do not run verifier after ResetMachineFunctionPass (#124799)

After we fall back from GlobalISel to SDAG, the verifier gets called,
which calls getReservedRegs which uses SIMachineFunctionInfo::usesAGPRs
which caches the result of UsesAGPRs. Because we have just fallen-back
the function is empty and it incorrectly gets cached to false. This
patch makes sure we don't try to run the verifier whilst the function is
empty.

Author: davemgreen

llvm/lib/CodeGen/TargetPassConfig.cpp

@@ -1039,11 +1039,13 @@ bool TargetPassConfig::addCoreISelPasses() {
 
     if (addGlobalInstructionSelect())
       return true;
+  }
 
-    // Pass to reset the MachineFunction if the ISel failed.
+  // Pass to reset the MachineFunction if the ISel failed. Outside of the above
+  // if so that the verifier is not added to it.
+  if (Selector == SelectorType::GlobalISel)
     addPass(createResetMachineFunctionPass(
         reportDiagnosticWhenGlobalISelFallback(), isGlobalISelAbortEnabled()));
-  }
 
   // Run the SDAG InstSelector, providing a fallback path when we do not want to
   // abort on not-yet-supported input.

llvm/test/CodeGen/AMDGPU/llvm.amdgcn.mfma.gfx950.ll

@@ -1,6 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
 ; RUN: llc -mtriple=amdgcn -mcpu=gfx950 -global-isel=0 < %s | FileCheck -enable-var-scope --check-prefixes=GCN,SDAG %s
-; RUN: llc -mtriple=amdgcn -mcpu=gfx950 -global-isel=1 -global-isel-abort=2 < %s | FileCheck -enable-var-scope --check-prefixes=GCN,GISEL %s
+; RUN: llc -mtriple=amdgcn -mcpu=gfx950 -global-isel=1 -global-isel-abort=2 -verify-machineinstrs < %s | FileCheck -enable-var-scope --check-prefixes=GCN,GISEL %s
 
 declare <4 x float> @llvm.amdgcn.mfma.f32.16x16x32.f16(<8 x half>, <8 x half>, <4 x float>, i32 immarg, i32 immarg, i32 immarg)
 declare <16 x float> @llvm.amdgcn.mfma.f32.32x32x16.f16(<8 x half>, <8 x half>, <16 x float>, i32 immarg, i32 immarg, i32 immarg)