Teach ScalarEvolution to simplify smax and umax when it can prove

that one operand is always greater than another.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101142 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 66 insertions, 2 deletions

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 307c83a2e1..a9a444f93a 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2117,7 +2117,13 @@ ScalarEvolution::getSMaxExpr(SmallVectorImpl<const SCEV *> &Ops) {
   // so, delete one.  Since we sorted the list, these values are required to
   // be adjacent.
   for (unsigned i = 0, e = Ops.size()-1; i != e; ++i)
-    if (Ops[i] == Ops[i+1]) {      //  X smax Y smax Y  -->  X smax Y
+    //  X smax Y smax Y  -->  X smax Y
+    //  X smax Y         -->  X, if X is always greater than Y
+    if (Ops[i] == Ops[i+1] ||
+        isKnownPredicate(ICmpInst::ICMP_SGE, Ops[i], Ops[i+1])) {
+      Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2);
+      --i; --e;
+    } else if (isKnownPredicate(ICmpInst::ICMP_SLE, Ops[i], Ops[i+1])) {
       Ops.erase(Ops.begin()+i, Ops.begin()+i+1);
       --i; --e;
     }
@@ -2216,7 +2222,13 @@ ScalarEvolution::getUMaxExpr(SmallVectorImpl<const SCEV *> &Ops) {
   // so, delete one.  Since we sorted the list, these values are required to
   // be adjacent.
   for (unsigned i = 0, e = Ops.size()-1; i != e; ++i)
-    if (Ops[i] == Ops[i+1]) {      //  X umax Y umax Y  -->  X umax Y
+    //  X umax Y umax Y  -->  X umax Y
+    //  X umax Y         -->  X, if X is always greater than Y
+    if (Ops[i] == Ops[i+1] ||
+        isKnownPredicate(ICmpInst::ICMP_UGE, Ops[i], Ops[i+1])) {
+      Ops.erase(Ops.begin()+i+1, Ops.begin()+i+2);
+      --i; --e;
+    } else if (isKnownPredicate(ICmpInst::ICMP_ULE, Ops[i], Ops[i+1])) {
       Ops.erase(Ops.begin()+i, Ops.begin()+i+1);
       --i; --e;
     }
diff --git a/test/Transforms/IndVarSimplify/eliminate-max.ll b/test/Transforms/IndVarSimplify/eliminate-max.ll
new file mode 100644
index 0000000000..c25bd0e354
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/eliminate-max.ll
@@ -0,0 +1,52 @@
+; RUN: opt < %s -S -indvars | grep {= icmp} | count 3
+; PR4914.ll
+
+; Indvars should be able to do range analysis and eliminate icmps.
+; There are two here which cannot be eliminated.
+; There's one that icmp which can be eliminated and which indvars currently
+; cannot eliminate, because it requires analyzing more than just the
+; range of the induction variable.
+
+@0 = private constant [4 x i8] c"%d\0A\00", align 1 ; <[4 x i8]*> [#uses=1]
+
+define i32 @main() nounwind {
+bb:
+  br label %bb1
+
+bb1:                                              ; preds = %bb14, %bb
+  %t = phi i32 [ 0, %bb ], [ %t19, %bb14 ]        ; <i32> [#uses=5]
+  %t2 = phi i32 [ 0, %bb ], [ %t18, %bb14 ]       ; <i32> [#uses=1]
+  %t3 = icmp slt i32 %t, 0                        ; <i1> [#uses=1]
+  br i1 %t3, label %bb7, label %bb4
+
+bb4:                                              ; preds = %bb1
+  %t5 = icmp sgt i32 %t, 255                      ; <i1> [#uses=1]
+  %t6 = select i1 %t5, i32 255, i32 %t            ; <i32> [#uses=1]
+  br label %bb7
+
+bb7:                                              ; preds = %bb4, %bb1
+  %t8 = phi i32 [ %t6, %bb4 ], [ 0, %bb1 ]        ; <i32> [#uses=1]
+  %t9 = sub i32 0, %t                             ; <i32> [#uses=3]
+  %t10 = icmp slt i32 %t9, 0                      ; <i1> [#uses=1]
+  br i1 %t10, label %bb14, label %bb11
+
+bb11:                                             ; preds = %bb7
+  %t12 = icmp sgt i32 %t9, 255                    ; <i1> [#uses=1]
+  %t13 = select i1 %t12, i32 255, i32 %t9         ; <i32> [#uses=1]
+  br label %bb14
+
+bb14:                                             ; preds = %bb11, %bb7
+  %t15 = phi i32 [ %t13, %bb11 ], [ 0, %bb7 ]     ; <i32> [#uses=1]
+  %t16 = add nsw i32 %t2, 255                     ; <i32> [#uses=1]
+  %t17 = add nsw i32 %t16, %t8                    ; <i32> [#uses=1]
+  %t18 = add nsw i32 %t17, %t15                   ; <i32> [#uses=2]
+  %t19 = add nsw i32 %t, 1                        ; <i32> [#uses=2]
+  %t20 = icmp slt i32 %t19, 1000000000            ; <i1> [#uses=1]
+  br i1 %t20, label %bb1, label %bb21
+
+bb21:                                             ; preds = %bb14
+  %t22 = call i32 (i8*, ...)* @printf(i8* noalias getelementptr inbounds ([4 x i8]* @0, i32 0, i32 0), i32 %t18) nounwind
+  ret i32 0
+}
+
+declare i32 @printf(i8* noalias nocapture, ...) nounwind