[IndVars] Canonicalize comparisons between non-negative values and indvars

-If there is a IndVar which is known to be non-negative, and there is a value which is also non-negative,
then signed and unsigned comparisons between them produce the same result. Both of those can be
seen in the same loop. To allow other optimizations to simplify them, we turn all instructions like

  %c = icmp slt i32 %iv, %b
to

  %c = icmp ult i32 %iv, %b

if both %iv and %b are known to be non-negative.

Differential Revision: https://reviews.llvm.org/D34979

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@307126 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyIndVar.cpp b/lib/Transforms/Utils/SimplifyIndVar.cpp
index ec8b0d426265afd862997f0a9c52efb2b6c90983..77f035a5a6508c518c50b4bd34432f1710136be6 100644 (file)
--- a/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -262,6 +262,10 @@ void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
     ICmp->setPredicate(InvariantPredicate);
     ICmp->setOperand(0, NewLHS);
     ICmp->setOperand(1, NewRHS);
+  } else if (ICmpInst::isSigned(Pred) &&
+             SE->isKnownNonNegative(S) && SE->isKnownNonNegative(X)) {
+    DEBUG(dbgs() << "INDVARS: Turn to unsigned comparison: " << *ICmp << '\n');
+    ICmp->setPredicate(ICmpInst::getUnsignedPredicate(Pred));
   } else
     return;
 

diff --git a/test/Analysis/ScalarEvolution/guards.ll b/test/Analysis/ScalarEvolution/guards.ll
index 52ad4dc73d417aa3c6aec3737b7bf9fe45f5cf45..d4b1f431ffc6a530fe49ab7d16c877939476c971 100644 (file)
--- a/test/Analysis/ScalarEvolution/guards.ll
+++ b/test/Analysis/ScalarEvolution/guards.ll
@@ -19,7 +19,7 @@ entry:
 loop:
 ; CHECK: loop:
 ; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
-; CHECK:  %iv.inc.cmp = icmp slt i32 %iv.inc, %len
+; CHECK:  %iv.inc.cmp = icmp ult i32 %iv.inc, %len
 ; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
 ; CHECK: leave:
 
@@ -41,7 +41,7 @@ leave:
 
 define void @test_2(i32 %n, i32* %len_buf) {
 ; CHECK-LABEL: @test_2(
-; CHECK:  [[LEN_SEXT:%[^ ]+]] = sext i32 %len to i64
+; CHECK:  [[LEN_ZEXT:%[^ ]+]] = zext i32 %len to i64
 ; CHECK:  br label %loop
 
 entry:
@@ -52,7 +52,7 @@ loop:
 ; CHECK: loop:
 ; CHECK:  %indvars.iv = phi i64 [ %indvars.iv.next, %loop ], [ 0, %entry ]
 ; CHECK:  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
-; CHECK:  %iv.inc.cmp = icmp slt i64 %indvars.iv.next, [[LEN_SEXT]]
+; CHECK:  %iv.inc.cmp = icmp ult i64 %indvars.iv.next, [[LEN_ZEXT]]
 ; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
 ; CHECK: leave:
 

diff --git a/test/Transforms/IndVarSimplify/canonicalize-cmp.ll b/test/Transforms/IndVarSimplify/canonicalize-cmp.ll
new file mode 100644 (file)
index 0000000..93dc968
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/canonicalize-cmp.ll
@@ -0,0 +1,52 @@
+; RUN: opt -S -indvars < %s | FileCheck %s
+
+; Check that we replace signed comparisons between non-negative values with
+; unsigned comparisons if we can.
+
+target datalayout = "n8:16:32:64"
+
+define i32 @test_01(i32 %a, i32 %b, i32* %p) {
+
+; CHECK-LABEL: @test_01(
+; CHECK-NOT:   icmp slt
+; CHECK:       %cmp1 = icmp ult i32 %iv, 100
+; CHECK:       %cmp2 = icmp ult i32 %iv, 100
+; CHECK-NOT:   %cmp3
+; CHECK:       %exitcond = icmp ne i32 %iv.next, 1000
+
+entry:
+  br label %loop.entry
+
+loop.entry:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop.be ]
+  %cmp1 = icmp slt i32 %iv, 100
+  br i1 %cmp1, label %b1, label %b2
+
+b1:
+  store i32 %iv, i32* %p
+  br label %merge
+
+b2:
+  store i32 %a, i32* %p
+  br label %merge
+
+merge:
+  %cmp2 = icmp ult i32 %iv, 100
+  br i1 %cmp2, label %b3, label %b4
+
+b3:
+  store i32 %iv, i32* %p
+  br label %loop.be
+
+b4:
+  store i32 %b, i32* %p
+  br label %loop.be
+
+loop.be:
+  %iv.next = add i32 %iv, 1
+  %cmp3 = icmp slt i32 %iv.next, 1000
+  br i1 %cmp3, label %loop.entry, label %exit
+
+exit:
+  ret i32 %iv
+}

diff --git a/test/Transforms/IndVarSimplify/eliminate-comparison.ll b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
index 612f01e3cadee616677df93d27794df4ce21ea11..a63617e62c0ea978bba4ad0fb10f95894feedb0f 100644 (file)
--- a/test/Transforms/IndVarSimplify/eliminate-comparison.ll
+++ b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
@@ -111,7 +111,7 @@ return:
 ; Indvars should not turn the second loop into an infinite one.
 
 ; CHECK-LABEL: @func_11(
-; CHECK: %tmp5 = icmp slt i32 %__key6.0, 10
+; CHECK: %tmp5 = icmp ult i32 %__key6.0, 10
 ; CHECK-NOT: br i1 true, label %noassert68, label %unrolledend
 
 define i32 @func_11() nounwind uwtable {
@@ -163,7 +163,7 @@ declare void @llvm.trap() noreturn nounwind
 
 ; In this case the second loop only has a single iteration, fold the header away
 ; CHECK-LABEL: @func_12(
-; CHECK: %tmp5 = icmp slt i32 %__key6.0, 10
+; CHECK: %tmp5 = icmp ult i32 %__key6.0, 10
 ; CHECK: br i1 true, label %noassert68, label %unrolledend
 define i32 @func_12() nounwind uwtable {
 entry:

diff --git a/test/Transforms/IndVarSimplify/widen-loop-comp.ll b/test/Transforms/IndVarSimplify/widen-loop-comp.ll
index b87cd0550192ed4073e609dc8897335a78bab0ee..2d24cd732ce84738e86827defb818ba8e03b4bdd 100644 (file)
--- a/test/Transforms/IndVarSimplify/widen-loop-comp.ll
+++ b/test/Transforms/IndVarSimplify/widen-loop-comp.ll
@@ -64,7 +64,7 @@ for.end:
 ; CHECK-LABEL: @test2
 ; CHECK: for.body4.us
 ; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
-; CHECK: %cmp2.us = icmp slt i64
+; CHECK: %cmp2.us = icmp ult i64
 ; CHECK-NOT: %2 = trunc i64 %indvars.iv.next to i32
 ; CHECK-NOT: %cmp2.us = icmp slt i32