[PATCH] D51404: [IndVars] Remove unreasonable checks in rewriteLoopExitValues

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: sanjoy, reames, skatkov.

A piece of logic in rewriteLoopExitValues has a weird check on number of
users which allowed an unprofitable transform in case if an instruction has
more than 6 users. It also used unsigned counters where boolean flags
would be sufficient.


https://reviews.llvm.org/D51404

Files:
  lib/Transforms/Scalar/IndVarSimplify.cpp
  test/Transforms/IndVarSimplify/dont-recompute.ll


Index: test/Transforms/IndVarSimplify/dont-recompute.ll
===================================================================
--- test/Transforms/IndVarSimplify/dont-recompute.ll
+++ test/Transforms/IndVarSimplify/dont-recompute.ll
@@ -67,3 +67,33 @@
 ; CHECK-NEXT: ret i32 %add.lcssa
   ret i32 %add
 }
+
+; CHECK-LABEL: @test3(
+define void @test3(i32 %m) nounwind uwtable {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %entry
+  %i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
+  %a.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
+  %add = add i32 %a.05, %m
+  mul i32 %add, 1
+  mul i32 %add, 1
+  mul i32 %add, 1
+  mul i32 %add, 1
+  mul i32 %add, 1
+  mul i32 %add, 1
+; CHECK: tail call void @func(i32 %add)
+  tail call void @func(i32 %add)
+  %inc = add nsw i32 %i.06, 1
+  %exitcond = icmp eq i32 %inc, 186
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body
+; CHECK: for.end:
+; CHECK-NOT: mul i32 %m, 186
+; CHECK:%add.lcssa = phi i32 [ %add, %for.body ]
+; CHECK-NEXT: tail call void @func(i32 %add.lcssa)
+  tail call void @func(i32 %add)
+  ret void
+}
Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -600,36 +600,35 @@
         //  - no use outside of the loop can take advantage of hoisting the
         //    computation out of the loop
         if (ExitValue->getSCEVType()>=scMulExpr) {
-          unsigned NumHardInternalUses = 0;
-          unsigned NumSoftExternalUses = 0;
-          unsigned NumUses = 0;
-          for (auto IB = Inst->user_begin(), IE = Inst->user_end();
-               IB != IE && NumUses <= 6; ++IB) {
-            Instruction *UseInstr = cast<Instruction>(*IB);
+          bool HasHardInternalUses = false;
+          bool HasSoftExternalUses = false;
+          for (auto *IB : Inst->users()) {
+            Instruction *UseInstr = cast<Instruction>(IB);
             unsigned Opc = UseInstr->getOpcode();
-            NumUses++;
             if (L->contains(UseInstr)) {
               if (Opc == Instruction::Call)
-                NumHardInternalUses++;
+                HasHardInternalUses = true;
             } else {
               if (Opc == Instruction::PHI) {
                 // Do not count the Phi as a use. LCSSA may have inserted
                 // plenty of trivial ones.
-                NumUses--;
-                for (auto PB = UseInstr->user_begin(),
-                          PE = UseInstr->user_end();
-                     PB != PE && NumUses <= 6; ++PB, ++NumUses) {
-                  unsigned PhiOpc = cast<Instruction>(*PB)->getOpcode();
-                  if (PhiOpc != Instruction::Call && PhiOpc != Instruction::Ret)
-                    NumSoftExternalUses++;
+                for (auto PB : UseInstr->users()) {
+                  unsigned PhiOpc = cast<Instruction>(*PB).getOpcode();
+                  if (PhiOpc != Instruction::Call &&
+                      PhiOpc != Instruction::Ret) {
+                    HasSoftExternalUses = true;
+                    break;
+                  }
                 }
                 continue;
               }
-              if (Opc != Instruction::Call && Opc != Instruction::Ret)
-                NumSoftExternalUses++;
+              if (Opc != Instruction::Call && Opc != Instruction::Ret) {
+                HasSoftExternalUses = true;
+                break;
+              }
             }
           }
-          if (NumUses <= 6 && NumHardInternalUses && !NumSoftExternalUses)
+          if (HasHardInternalUses && !HasSoftExternalUses)
             continue;
         }
 


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