This patch adds the X86FixupLEAs pass, which will reduce instruction

latency for certain models of the Intel Atom family, by converting
instructions into their equivalent LEA instructions, when it is both
useful and possible to do so.

llvm-svn: 180573

1 files changed, 51 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/atom-fixup-lea3.ll b/llvm/test/CodeGen/X86/atom-fixup-lea3.ll
new file mode 100644
index 00000000000..311b0b30216
--- /dev/null
+++ b/llvm/test/CodeGen/X86/atom-fixup-lea3.ll
@@ -0,0 +1,51 @@
+; RUN: llc < %s -mcpu=atom -mtriple=i686-linux | FileCheck %s
+; CHECK: addl ([[reg:%[a-z]+]])
+; CHECK-NEXT: addl $4, [[reg]]
+
+; Test for the FixupLEAs pre-emit pass.
+; An LEA should NOT be substituted for the ADD instruction
+; that increments the array pointer if it is greater than 5 instructions
+; away from the memory reference that uses it.
+
+; Original C code: clang -m32 -S -O2
+;int test(int n, int * array, int * m, int * array2)
+;{
+;  int i, j = 0;
+;  int sum = 0;
+;  for (i = 0, j = 0; i < n;) {
+;    ++i;
+;    *m += array2[j++];
+;    sum += array[i];
+;  }
+;  return sum;
+;}
+
+define i32 @test(i32 %n, i32* nocapture %array, i32* nocapture %m, i32* nocapture %array2) #0 {
+entry:
+  %cmp7 = icmp sgt i32 %n, 0
+  br i1 %cmp7, label %for.body.lr.ph, label %for.end
+
+for.body.lr.ph:                                   ; preds = %entry
+  %.pre = load i32* %m, align 4
+  br label %for.body
+
+for.body:                                         ; preds = %for.body, %for.body.lr.ph
+  %0 = phi i32 [ %.pre, %for.body.lr.ph ], [ %add, %for.body ]
+  %sum.010 = phi i32 [ 0, %for.body.lr.ph ], [ %add3, %for.body ]
+  %j.09 = phi i32 [ 0, %for.body.lr.ph ], [ %inc1, %for.body ]
+  %inc1 = add nsw i32 %j.09, 1
+  %arrayidx = getelementptr inbounds i32* %array2, i32 %j.09
+  %1 = load i32* %arrayidx, align 4
+  %add = add nsw i32 %0, %1
+  store i32 %add, i32* %m, align 4
+  %arrayidx2 = getelementptr inbounds i32* %array, i32 %inc1
+  %2 = load i32* %arrayidx2, align 4
+  %add3 = add nsw i32 %2, %sum.010
+  %exitcond = icmp eq i32 %inc1, %n
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:                                          ; preds = %for.body, %entry
+  %sum.0.lcssa = phi i32 [ 0, %entry ], [ %add3, %for.body ]
+  ret i32 %sum.0.lcssa
+}
+