[GlobalISel] Do not run verifier after ResetMachineFunctionPass (llvm#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.

(cherry picked from commit 66e0498)

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)