Add LiveRangeShrink pass to shrink live range within BB.

Summary: LiveRangeShrink pass moves instruction right after the definition with the same BB if the instruction and its operands all have more than one use. This pass is inexpensive and guarantees optimal live-range within BB.

Reviewers: davidxl, wmi, hfinkel, MatzeB, andreadb

Reviewed By: MatzeB, andreadb

Subscribers: hiraditya, jyknight, sanjoy, skatkov, gberry, jholewinski, qcolombet, javed.absar, krytarowski, atrick, spatel, RKSimon, andreadb, MatzeB, mehdi_amini, mgorny, efriedma, davide, dberlin, llvm-commits

Differential Revision: https://reviews.llvm.org/D32563

llvm-svn: 304371

1 files changed, 57 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/lrshrink.ll b/llvm/test/CodeGen/X86/lrshrink.ll
new file mode 100644
index 00000000000..a9cf086dbd9
--- /dev/null
+++ b/llvm/test/CodeGen/X86/lrshrink.ll
@@ -0,0 +1,57 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s
+
+; Checks if "%7 = add nuw nsw i64 %4, %2" is moved before the last call
+; to minimize live-range.
+
+define i64 @test(i1 %a, i64 %r1, i64 %r2, i64 %s1, i64 %s2, i64 %t1, i64 %t2) {
+entry:
+  br i1 %a, label %then, label %else
+
+then:
+  br label %else
+
+else:
+  %0 = phi i64 [ 4, %entry ], [ 10, %then ]
+  %r = phi i64 [ %r1, %entry ], [ %r2, %then ]
+  %s = phi i64 [ %s1, %entry ], [ %s2, %then ]
+  %t = phi i64 [ %t1, %entry ], [ %t2, %then ]
+; CHECK-LABEL: test:
+; CHECK: add
+; CHECK: add
+; CHECK: call
+; CHECK: add
+; CHECK: call
+; CHECK: add
+; CHECK: call
+; CHECK: add
+  %1 = tail call i32 @_Z3foov()
+  %2 = zext i32 %1 to i64
+  %3 = tail call i32 @_Z3foov()
+  %4 = zext i32 %3 to i64
+  %5 = tail call i32 @_Z3foov()
+  %6 = zext i32 %5 to i64
+  %7 = add nuw nsw i64 %0, %r
+  tail call void @llvm.dbg.value(metadata i64 %7, i64 0, metadata !5, metadata !DIExpression()), !dbg !6
+  %8 = add nuw nsw i64 %2, %7
+  %9 = add nuw nsw i64 %4, %8
+  %10 = add nuw nsw i64 %6, %9
+  %11 = add nuw nsw i64 %s, %t
+  tail call void @llvm.dbg.value(metadata i64 %11, i64 0, metadata !5, metadata !DIExpression()), !dbg !6
+  %12 = add nuw nsw i64 %10, %11
+  ret i64 %12
+}
+
+declare i32 @_Z3foov()
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!1, !2}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, emissionKind: FullDebug)
+!1 = !{i32 2, !"Dwarf Version", i32 4}
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !DIFile(filename: "a.c", directory: "./")
+!4 = distinct !DISubprogram(name: "test", scope: !3, unit: !0)
+!5 = !DILocalVariable(name: "x", scope: !4)
+!6 = !DILocation(line: 4, scope: !4)