[CVP] Process binary operations even when def is local

Summary:
This patch adds processing of binary operations when the def of operands are in
the same block (i.e. local processing).

Earlier we bailed out in such cases (the bail out was introduced in rL252032)
because LVI at that time was more precise about context at the end of basic
blocks, which implied local def and use analysis didn't benefit CVP.

Since then we've added support for LVI in presence of assumes and guards. The
test cases added show how local def processing in CVP helps adding more
information to the ashr, sdiv, srem and add operators.

Note: processCmp which suffers from the same problem will
be handled in a later patch.

Reviewers: philip, apilipenko, SjoerdMeijer, hfinkel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38766

llvm-svn: 315634

llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp

@@ -335,18 +335,6 @@ static bool processCallSite(CallSite CS, LazyValueInfo *LVI) {
   return true;
 }
 
-// Helper function to rewrite srem and sdiv. As a policy choice, we choose not
-// to waste compile time on anything where the operands are local defs.  While
-// LVI can sometimes reason about such cases, it's not its primary purpose.
-static bool hasLocalDefs(BinaryOperator *SDI) {
-  for (Value *O : SDI->operands()) {
-    auto *I = dyn_cast<Instruction>(O);
-    if (I && I->getParent() == SDI->getParent())
-      return true;
-  }
-  return false;
-}
-
 static bool hasPositiveOperands(BinaryOperator *SDI, LazyValueInfo *LVI) {
   Constant *Zero = ConstantInt::get(SDI->getType(), 0);
   for (Value *O : SDI->operands()) {
@@ -358,7 +346,7 @@ static bool hasPositiveOperands(BinaryOperator *SDI, LazyValueInfo *LVI) {
 }
 
 static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
-  if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI) ||
+  if (SDI->getType()->isVectorTy() ||
       !hasPositiveOperands(SDI, LVI))
     return false;
 
@@ -376,7 +364,7 @@ static bool processSRem(BinaryOperator *SDI, LazyValueInfo *LVI) {
 /// conditions, this can sometimes prove conditions instcombine can't by
 /// exploiting range information.
 static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
-  if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI) ||
+  if (SDI->getType()->isVectorTy() ||
       !hasPositiveOperands(SDI, LVI))
     return false;
 
@@ -391,7 +379,7 @@ static bool processSDiv(BinaryOperator *SDI, LazyValueInfo *LVI) {
 }
 
 static bool processAShr(BinaryOperator *SDI, LazyValueInfo *LVI) {
-  if (SDI->getType()->isVectorTy() || hasLocalDefs(SDI))
+  if (SDI->getType()->isVectorTy())
     return false;
 
   Constant *Zero = ConstantInt::get(SDI->getType(), 0);
@@ -415,7 +403,7 @@ static bool processAdd(BinaryOperator *AddOp, LazyValueInfo *LVI) {
   if (DontProcessAdds)
     return false;
 
-  if (AddOp->getType()->isVectorTy() || hasLocalDefs(AddOp))
+  if (AddOp->getType()->isVectorTy())
     return false;
 
   bool NSW = AddOp->hasNoSignedWrap();

llvm/test/Transforms/CorrelatedValuePropagation/add.ll

@@ -307,3 +307,26 @@ exit:
   ret void
 }
 
+; single basic block loop
+; because the loop exit condition is SLT, we can supplement the iv add
+; (iv.next def) with an nsw.
+; CHECK-LABEL: @test16(
+define i32 @test16(i32* %n, i32* %a) {
+preheader:
+  br label %loop
+
+loop:
+; CHECK: %iv.next = add nsw i32 %iv, 1
+  %iv = phi i32 [ 0, %preheader ], [ %iv.next, %loop ]
+  %acc = phi i32 [ 0, %preheader ], [ %acc.curr, %loop ]
+  %x = load atomic i32, i32* %a unordered, align 8
+  fence acquire
+  %acc.curr = add i32 %acc, %x
+  %iv.next = add i32 %iv, 1
+  %nval = load atomic i32, i32* %n unordered, align 8
+  %cmp = icmp slt i32 %iv.next, %nval
+  br i1 %cmp, label %loop, label %exit
+
+exit:
+  ret i32 %acc.curr
+}

llvm/test/Transforms/CorrelatedValuePropagation/ashr.ll

@@ -54,3 +54,46 @@ bb:
 exit:
   ret void
 }
+
+; looping case where loop has exactly one block
+; at the point of ashr, we know that the operand is always greater than 0,
+; because of the guard before it, so we can transform it to lshr.
+declare void @llvm.experimental.guard(i1,...)
+; CHECK-LABEL: @test4
+define void @test4(i32 %n) {
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+; CHECK: lshr i32 %a, 1
+  %a = phi i32 [ %n, %entry ], [ %shr, %loop ]
+  %cond = icmp sgt i32 %a, 2
+  call void(i1,...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
+  %shr = ashr i32 %a, 1
+  br i1 %cond, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+; same test as above with assume instead of guard.
+declare void @llvm.assume(i1)
+; CHECK-LABEL: @test5
+define void @test5(i32 %n) {
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+; CHECK: lshr i32 %a, 1
+  %a = phi i32 [ %n, %entry ], [ %shr, %loop ]
+  %cond = icmp sgt i32 %a, 4
+  call void @llvm.assume(i1 %cond)
+  %shr = ashr i32 %a, 1
+  %loopcond = icmp sgt i32 %shr, 8
+  br i1 %loopcond, label %loop, label %exit
+
+exit:
+  ret void
+}

llvm/test/Transforms/CorrelatedValuePropagation/sdiv.ll

@@ -52,3 +52,46 @@ bb:
 exit:
   ret void
 }
+
+; looping case where loop has exactly one block
+; at the point of sdiv, we know that %a is always greater than 0,
+; because of the guard before it, so we can transform it to udiv.
+declare void @llvm.experimental.guard(i1,...)
+; CHECK-LABEL: @test4
+define void @test4(i32 %n) {
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+; CHECK: udiv i32 %a, 6
+  %a = phi i32 [ %n, %entry ], [ %div, %loop ]
+  %cond = icmp sgt i32 %a, 4
+  call void(i1,...) @llvm.experimental.guard(i1 %cond) [ "deopt"() ]
+  %div = sdiv i32 %a, 6
+  br i1 %cond, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+; same test as above with assume instead of guard.
+declare void @llvm.assume(i1)
+; CHECK-LABEL: @test5
+define void @test5(i32 %n) {
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+; CHECK: udiv i32 %a, 6
+  %a = phi i32 [ %n, %entry ], [ %div, %loop ]
+  %cond = icmp sgt i32 %a, 4
+  call void @llvm.assume(i1 %cond)
+  %div = sdiv i32 %a, 6
+  %loopcond = icmp sgt i32 %div, 8
+  br i1 %loopcond, label %loop, label %exit
+
+exit:
+  ret void
+}

llvm/test/Transforms/CorrelatedValuePropagation/srem.ll

@@ -19,3 +19,26 @@ if.then:
 if.end:
   ret void
 }
+
+; looping case where loop has exactly one block
+; at the point of srem, we know that %a is always greater than 0,
+; because of the assume before it, so we can transform it to urem.
+declare void @llvm.assume(i1)
+; CHECK-LABEL: @test4
+define void @test4(i32 %n) {
+entry:
+  %cmp = icmp sgt i32 %n, 0
+  br i1 %cmp, label %loop, label %exit
+
+loop:
+; CHECK: urem i32 %a, 6
+  %a = phi i32 [ %n, %entry ], [ %rem, %loop ]
+  %cond = icmp sgt i32 %a, 4
+  call void @llvm.assume(i1 %cond)
+  %rem = srem i32 %a, 6
+  %loopcond = icmp sgt i32 %rem, 8
+  br i1 %loopcond, label %loop, label %exit
+
+exit:
+  ret void
+}