Teach IndVarSimplify how to eliminate comparisons involving induction

variables. For example, with code like this:

  for (i=0;i<n;++i)
    if (i<n)
      x[i] = 0;

IndVarSimplify will now recognize that i is always less than n inside
the loop, and eliminate the if.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101000 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 40 insertions, 0 deletions

diff --git a/test/Transforms/IndVarSimplify/eliminate-comparison.ll b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
new file mode 100644
index 0000000..d156974
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/eliminate-comparison.ll
@@ -0,0 +1,40 @@
+; RUN: opt -indvars -S < %s | FileCheck %s
+
+; Indvars should be able to simplify simple comparisons involving
+; induction variables.
+
+; CHECK: %cond = and i1 %tobool.not, true
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+
+@X = external global [0 x double]
+
+define void @foo(i64 %n, i32* nocapture %p) nounwind {
+entry:
+  %cmp9 = icmp sgt i64 %n, 0
+  br i1 %cmp9, label %pre, label %return
+
+pre:
+  %t3 = load i32* %p
+  %tobool.not = icmp ne i32 %t3, 0
+  br label %loop
+
+loop:
+  %i = phi i64 [ 0, %pre ], [ %inc, %for.inc ]
+  %cmp6 = icmp slt i64 %i, %n
+  %cond = and i1 %tobool.not, %cmp6
+  br i1 %cond, label %if.then, label %for.inc
+
+if.then:
+  %arrayidx = getelementptr [0 x double]* @X, i64 0, i64 %i
+  store double 3.200000e+00, double* %arrayidx
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i64 %i, 1
+  %exitcond = icmp sge i64 %inc, %n
+  br i1 %exitcond, label %return, label %loop
+
+return:
+  ret void
+}