[TTI] Teach the cost heuristic how to query TLI to check if a zext/trunc is 'free' for the target.

Now that SimplifyCFG uses TTI for the cost heuristic, we can teach BasicTTIImpl
how to query TLI in order to get a more accurate cost for truncates and
zero-extends.

Before this patch, the basic cost heuristic in TargetTransformInfoImplCRTPBase
would have conservatively returned a 'default' TCC_Basic for all zero-extends,
and TCC_Free for truncates on native types.

This patch improves the heuristic so that we query TLI (if available) to get
more accurate answers. If TLI is available, then methods 'isZExtFree' and
'isTruncateFree' can be used to check if a zext/trunc is free for the target.

Added more test cases to SimplifyCFG/X86/speculate-cttz-ctlz.ll.
With this change, SimplifyCFG is now able to speculate a 'cheap' cttz/ctlz
immediately followed by a free zext/trunc.

Differential Revision: http://reviews.llvm.org/D7585

llvm-svn: 228923

1 files changed, 189 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll b/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
index 6873d7da788..69f6c69059d 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/speculate-cttz-ctlz.ll
@@ -133,6 +133,195 @@ cond.end:                                         ; preds = %entry, %cond.true
   ret i16 %cond
 }
 
+; The following tests verify that calls to cttz/ctlz are speculated even if
+; basic block %cond.true has an extra zero extend/truncate which is "free"
+; for the target.
+
+define i64 @test1e(i32 %x) {
+; ALL-LABEL: @test1e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
+; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
+; ALL: [[ZEXT:%[A-Za-z0-9]+]] = zext i32 [[CTTZ]] to i64
+; BMI-NEXT: select i1 [[COND]], i64 32, i64 [[ZEXT]]
+; LZCNT-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i32 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
+  %phitmp2 = zext i32 %0 to i64
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i64 [ %phitmp2, %cond.true ], [ 32, %entry ]
+  ret i64 %cond
+}
+
+define i32 @test2e(i64 %x) {
+; ALL-LABEL: @test2e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
+; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
+; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTTZ]] to i32
+; BMI-NEXT: select i1 [[COND]], i32 64, i32 [[TRUNC]]
+; LZCNT-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i64 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
+  %cast = trunc i64 %0 to i32
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i32 [ %cast, %cond.true ], [ 64, %entry ]
+  ret i32 %cond
+}
+
+define i64 @test3e(i32 %x) {
+; ALL-LABEL: @test3e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
+; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
+; ALL: [[ZEXT:%[A-Za-z0-9]+]] = zext i32 [[CTLZ]] to i64
+; LZCNT-NEXT: select i1 [[COND]], i64 32, i64 [[ZEXT]]
+; BMI-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i32 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
+  %phitmp2 = zext i32 %0 to i64
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i64 [ %phitmp2, %cond.true ], [ 32, %entry ]
+  ret i64 %cond
+}
+
+define i32 @test4e(i64 %x) {
+; ALL-LABEL: @test4e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
+; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
+; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTLZ]] to i32
+; LZCNT-NEXT: select i1 [[COND]], i32 64, i32 [[TRUNC]]
+; BMI-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i64 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
+  %cast = trunc i64 %0 to i32
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i32 [ %cast, %cond.true ], [ 64, %entry ]
+  ret i32 %cond
+}
+
+define i16 @test5e(i64 %x) {
+; ALL-LABEL: @test5e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
+; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
+; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTLZ]] to i16
+; LZCNT-NEXT: select i1 [[COND]], i16 64, i16 [[TRUNC]]
+; BMI-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i64 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i64 @llvm.ctlz.i64(i64 %x, i1 true)
+  %cast = trunc i64 %0 to i16
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i16 [ %cast, %cond.true ], [ 64, %entry ]
+  ret i16 %cond
+}
+
+define i16 @test6e(i32 %x) {
+; ALL-LABEL: @test6e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
+; ALL: [[CTLZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
+; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i32 [[CTLZ]] to i16
+; LZCNT-NEXT: select i1 [[COND]], i16 32, i16 [[TRUNC]]
+; BMI-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i32 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true)
+  %cast = trunc i32 %0 to i16
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i16 [ %cast, %cond.true ], [ 32, %entry ]
+  ret i16 %cond
+}
+
+define i16 @test7e(i64 %x) {
+; ALL-LABEL: @test7e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i64 %x, 0
+; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
+; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i64 [[CTTZ]] to i16
+; BMI-NEXT: select i1 [[COND]], i16 64, i16 [[TRUNC]]
+; LZCNT-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i64 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i64 @llvm.cttz.i64(i64 %x, i1 true)
+  %cast = trunc i64 %0 to i16
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i16 [ %cast, %cond.true ], [ 64, %entry ]
+  ret i16 %cond
+}
+
+define i16 @test8e(i32 %x) {
+; ALL-LABEL: @test8e(
+; ALL: [[COND:%[A-Za-z0-9]+]] = icmp eq i32 %x, 0
+; ALL: [[CTTZ:%[A-Za-z0-9]+]] = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
+; ALL: [[TRUNC:%[A-Za-z0-9]+]] = trunc i32 [[CTTZ]] to i16
+; BMI-NEXT: select i1 [[COND]], i16 32, i16 [[TRUNC]]
+; LZCNT-NOT: select
+; GENERIC-NOT: select
+; ALL: ret
+entry:
+  %tobool = icmp eq i32 %x, 0
+  br i1 %tobool, label %cond.end, label %cond.true
+
+cond.true:                                        ; preds = %entry
+  %0 = tail call i32 @llvm.cttz.i32(i32 %x, i1 true)
+  %cast = trunc i32 %0 to i16
+  br label %cond.end
+
+cond.end:                                         ; preds = %entry, %cond.true
+  %cond = phi i16 [ %cast, %cond.true ], [ 32, %entry ]
+  ret i16 %cond
+}
+
+
 declare i64 @llvm.ctlz.i64(i64, i1)
 declare i32 @llvm.ctlz.i32(i32, i1)
 declare i16 @llvm.ctlz.i16(i16, i1)