[PATCH] D149030: [PPCMIPeephole] Fix incorrect compare elimination

[Fangrui Song via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG398d68f624d6: [PPCMIPeephole] Fix incorrect compare elimination (authored by MaskRay).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149030/new/

https://reviews.llvm.org/D149030

Files:
  llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
  llvm/test/CodeGen/PowerPC/cmp_elimination.ll


Index: llvm/test/CodeGen/PowerPC/cmp_elimination.ll
===================================================================
--- llvm/test/CodeGen/PowerPC/cmp_elimination.ll
+++ llvm/test/CodeGen/PowerPC/cmp_elimination.ll
@@ -779,6 +779,29 @@
   ret void
 }
 
+;; The result of %cmp may change in a tail call. Don't lift %cmp to the entry block.
+; CHECK-LABEL: func_tailrecurse:
+; CHECK-NOT:     cmp
+; CHECK:       .LBB{{.*}}:
+; CHECK:         cmplw
+; CHECK:         blt
+define fastcc zeroext i32 @func_tailrecurse(i32 zeroext %a, i32 zeroext %b) {
+entry:
+  br label %tailrecurse
+
+tailrecurse:                                      ; preds = %tailrecurse, %entry
+  %a.tr = phi i32 [ %a, %entry ], [ %b.tr, %tailrecurse ]
+  %b.tr = phi i32 [ %b, %entry ], [ %a.tr, %tailrecurse ]
+  %cmp = icmp ult i32 %a.tr, %b.tr
+  %conv = zext i1 %cmp to i32
+  %ignore = call signext i32 (i32) @func(i32 %conv)
+  br i1 %cmp, label %tailrecurse, label %if.end
+
+if.end:                                           ; preds = %tailrecurse
+  %sub = sub nsw i32 %a.tr, %b.tr
+  ret i32 %sub
+}
+
 declare void @dummy1()
 declare void @dummy2()
 declare void @dummy3()
Index: llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
===================================================================
--- llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
+++ llvm/lib/Target/PowerPC/PPCMIPeephole.cpp
@@ -1315,7 +1315,7 @@
     if (isEligibleBB(*Pred1MBB) && isEligibleForMoveCmp(*Pred2MBB)) {
       // We assume Pred1MBB is the BB containing the compare to be merged and
       // Pred2MBB is the BB to which we will append a compare instruction.
-      // Hence we can proceed as is.
+      // Proceed as is if Pred1MBB is different from MBB.
     }
     else if (isEligibleBB(*Pred2MBB) && isEligibleForMoveCmp(*Pred1MBB)) {
       // We need to swap Pred1MBB and Pred2MBB to canonicalize.
@@ -1323,6 +1323,9 @@
     }
     else return false;
 
+    if (Pred1MBB == &MBB)
+      return false;
+
     // Here, Pred2MBB is the BB to which we need to append a compare inst.
     // We cannot move the compare instruction if operands are not available
     // in Pred2MBB (i.e. defined in MBB by an instruction other than PHI).


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