[NFC][AMDGPU] IGLP: Fixes for unsigned int handling

Fixes unsigned int underflows in
`MFMASmallGemmSingleWaveOpt::applyIGLPStrategy`.

Author: ro-i

llvm/lib/Target/AMDGPU/AMDGPUIGroupLP.cpp

@@ -2183,7 +2183,7 @@ bool MFMASmallGemmSingleWaveOpt::applyIGLPStrategy(
   SG->initSchedGroup(SyncedInstrs[SG->getSyncID()]);
 
   // Interleave MFMA with DS_READ prefetch
-  for (unsigned I = 0; I < DSRCount - 4; ++I) {
+  for (unsigned I = 4; I < DSRCount; ++I) {
     SG = &SyncedSchedGroups[PipelineSyncID].emplace_back(
         SchedGroupMask::DS_READ, 1, PipelineSyncID, DAG, TII);
     SG->initSchedGroup(SyncedInstrs[SG->getSyncID()]);
@@ -2196,7 +2196,7 @@ bool MFMASmallGemmSingleWaveOpt::applyIGLPStrategy(
   // Phase 2a: Loop carried dependency with V_PERM
   // Schedule VPerm & DS_WRITE as closely as possible to the VMEM_READ they
   // depend on. Interleave MFMA to keep XDL unit busy throughout.
-  for (unsigned I = 0; I < DSWWithPermCount - DSWWithSharedVMEMCount; ++I) {
+  for (unsigned I = DSWWithSharedVMEMCount; I < DSWWithPermCount; ++I) {
     SG = &SyncedSchedGroups[PipelineSyncID].emplace_back(
         SchedGroupMask::VALU, 4, PipelineSyncID, DAG, TII);
     SG->addRule(std::make_shared<IsPermForDSW>(TII, SG->getSGID(), true));
@@ -2233,7 +2233,7 @@ bool MFMASmallGemmSingleWaveOpt::applyIGLPStrategy(
   // Phase 2b: Loop carried dependency without V_PERM
   // Schedule DS_WRITE as closely as possible to the VMEM_READ they depend on.
   // Interleave MFMA to keep XDL unit busy throughout.
-  for (unsigned I = 0; I < DSWCount - DSWWithPermCount; I++) {
+  for (unsigned I = DSWWithPermCount; I < DSWCount; I++) {
     SG = &SyncedSchedGroups[PipelineSyncID].emplace_back(
         SchedGroupMask::DS_WRITE, 1, PipelineSyncID, DAG, TII);
     SG->initSchedGroup(SyncedInstrs[SG->getSyncID()]);