Thread comparisons over udiv/sdiv/ashr/lshr exact and lshr nuw/nsw whenever

possible. This goes into instcombine and instsimplify because instsimplify
doesn't need to check hasOneUse since it returns (almost exclusively) constants.

This fixes PR9343 #4 #5 and #8!

llvm-svn: 127064

lib/Analysis/InstructionSimplify.cpp

@@ -1344,7 +1344,7 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
   // the compare, and if only one of them is then we moved it to RHS already.
   if (isa<AllocaInst>(LHS) && (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
                                isa<ConstantPointerNull>(RHS)))
-    // We already know that LHS != LHS.
+    // We already know that LHS != RHS.
     return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
 
   // If we are comparing with zero then try hard since this is a common case.
@@ -1700,6 +1700,38 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
     }
   }
 
+  if (MaxRecurse && LBO && RBO && LBO->getOpcode() == RBO->getOpcode() &&
+      LBO->getOperand(1) == RBO->getOperand(1)) {
+    switch (LBO->getOpcode()) {
+    default: break;
+    case Instruction::UDiv:
+    case Instruction::LShr:
+      if (ICmpInst::isSigned(Pred))
+        break;
+      // fall-through
+    case Instruction::SDiv:
+    case Instruction::AShr:
+      if (!LBO->isExact() && !RBO->isExact())
+        break;
+      if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
+                                      RBO->getOperand(0), TD, DT, MaxRecurse-1))
+        return V;
+      break;
+    case Instruction::Shl: {
+      bool NUW = LBO->hasNoUnsignedWrap() && LBO->hasNoUnsignedWrap();
+      bool NSW = LBO->hasNoSignedWrap() && RBO->hasNoSignedWrap();
+      if (!NUW && !NSW)
+        break;
+      if (!NSW && ICmpInst::isSigned(Pred))
+        break;
+      if (Value *V = SimplifyICmpInst(Pred, LBO->getOperand(0),
+                                      RBO->getOperand(0), TD, DT, MaxRecurse-1))
+        return V;
+      break;
+    }
+    }
+  }
+
   // If the comparison is with the result of a select instruction, check whether
   // comparing with either branch of the select always yields the same value.
   if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))

lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -2393,6 +2393,27 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
           }
         }
         break;
+      case Instruction::UDiv:
+      case Instruction::LShr:
+        if (I.isSigned())
+          break;
+        // fall-through
+      case Instruction::SDiv:
+      case Instruction::AShr:
+        if (!BO0->isExact() && !BO1->isExact())
+          break;
+        return new ICmpInst(I.getPredicate(), BO0->getOperand(0),
+                            BO1->getOperand(0));
+      case Instruction::Shl: {
+        bool NUW = BO0->hasNoUnsignedWrap() && BO1->hasNoUnsignedWrap();
+        bool NSW = BO0->hasNoSignedWrap() && BO1->hasNoSignedWrap();
+        if (!NUW && !NSW)
+          break;
+        if (!NSW && I.isSigned())
+          break;
+        return new ICmpInst(I.getPredicate(), BO0->getOperand(0),
+                            BO1->getOperand(0));
+      }
       }
     }
   }

test/Transforms/InstCombine/icmp.ll

@@ -419,3 +419,49 @@ define i1 @test43(i32 %X, i32 %Y) {
   %B = icmp slt i32 %Y, %A
   ret i1 %B
 }
+
+; CHECK: @test44
+; CHECK: %B = icmp sgt i32 %Y, -1
+define i1 @test44(i32 %X, i32 %Y) {
+  %A = srem i32 %X, %Y
+  %B = icmp slt i32 %A, %Y
+  ret i1 %B
+}
+
+; CHECK: @test45
+; CHECK: %B = icmp slt i32 %Y, 0
+define i1 @test45(i32 %X, i32 %Y) {
+  %A = srem i32 %X, %Y
+  %B = icmp slt i32 %Y, %A
+  ret i1 %B
+}
+
+; PR9343 #4
+; CHECK: @test46
+; CHECK: %C = icmp ult i32 %X, %Y
+define i1 @test46(i32 %X, i32 %Y, i32 %Z) {
+  %A = ashr exact i32 %X, %Z
+  %B = ashr exact i32 %Y, %Z
+  %C = icmp ult i32 %A, %B
+  ret i1 %C
+}
+
+; PR9343 #5
+; CHECK: @test47
+; CHECK: %C = icmp ugt i32 %X, %Y
+define i1 @test47(i32 %X, i32 %Y, i32 %Z) {
+  %A = ashr exact i32 %X, %Z
+  %B = ashr exact i32 %Y, %Z
+  %C = icmp ugt i32 %A, %B
+  ret i1 %C
+}
+
+; PR9343 #8
+; CHECK: @test48
+; CHECK: %C = icmp eq i32 %X, %Y
+define i1 @test48(i32 %X, i32 %Y, i32 %Z) {
+  %A = sdiv exact i32 %X, %Z
+  %B = sdiv exact i32 %Y, %Z
+  %C = icmp eq i32 %A, %B
+  ret i1 %C
+}

test/Transforms/InstSimplify/compare.ll

@@ -261,6 +261,15 @@ define i1 @udiv1(i32 %X) {
 ; CHECK: ret i1 true
 }
 
+define i1 @udiv2(i32 %X, i32 %Y, i32 %Z) {
+; CHECK: @udiv2
+  %A = udiv exact i32 10, %Z
+  %B = udiv exact i32 20, %Z
+  %C = icmp ult i32 %A, %B
+  ret i1 %C
+; CHECK: ret i1 true
+}
+
 define i1 @sdiv1(i32 %X) {
 ; CHECK: @sdiv1
   %A = sdiv i32 %X, 1000000