Improve instcombine's handling of integer min and max in two ways:

 - Recognize expressions like "x > -1 ? x : 0" as min/max and turn them
   into expressions like "x < 0 ? 0 : x", which is easily recognizable
   as a min/max operation.
 - Refrain from folding expression like "y/2 < 1" to "y < 2" when the
   comparison is being used as part of a min or max idiom, like
   "y/2 < 1 ? 1 : y/2". In that case, the division has another use, so
   folding doesn't eliminate it, and obfuscates the min/max, making it
   harder to recognize as a min/max operation.

These benefit ScalarEvolution, CodeGen, and anything else that wants to
recognize integer min and max.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56246 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 107 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/adjust-for-sminmax.ll b/test/Transforms/InstCombine/adjust-for-sminmax.ll
new file mode 100644
index 0000000000..9328ad3649
--- /dev/null
+++ b/test/Transforms/InstCombine/adjust-for-sminmax.ll
@@ -0,0 +1,85 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {icmp s\[lg\]t i32 %n, 0} | count 16
+
+; Instcombine should recognize that this code can be adjusted
+; to fit the canonical smax/smin pattern.
+
+define i32 @floor_a(i32 %n) {
+  %t = icmp sgt i32 %n, -1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_a(i32 %n) {
+  %t = icmp slt i32 %n, 1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_b(i32 %n) {
+  %t = icmp sgt i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_b(i32 %n) {
+  %t = icmp slt i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_c(i32 %n) {
+  %t = icmp sge i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_c(i32 %n) {
+  %t = icmp sle i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_d(i32 %n) {
+  %t = icmp sge i32 %n, 1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_d(i32 %n) {
+  %t = icmp sle i32 %n, -1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_e(i32 %n) {
+  %t = icmp sgt i32 %n, -1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_e(i32 %n) {
+  %t = icmp slt i32 %n, 1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_f(i32 %n) {
+  %t = icmp sgt i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_f(i32 %n) {
+  %t = icmp slt i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_g(i32 %n) {
+  %t = icmp sge i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_g(i32 %n) {
+  %t = icmp sle i32 %n, 0
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @floor_h(i32 %n) {
+  %t = icmp sge i32 %n, 1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
+define i32 @ceil_h(i32 %n) {
+  %t = icmp sle i32 %n, -1
+  %m = select i1 %t, i32 %n, i32 0
+  ret i32 %m
+}
diff --git a/test/Transforms/InstCombine/preserve-sminmax.ll b/test/Transforms/InstCombine/preserve-sminmax.ll
new file mode 100644
index 0000000000..24fb7dabe3
--- /dev/null
+++ b/test/Transforms/InstCombine/preserve-sminmax.ll
@@ -0,0 +1,22 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep { i32 \[%\]sd, \[\[:alnum:\]\]* \\?1\\>} | count 4
+
+; Instcombine normally would fold the sdiv into the comparison,
+; making "icmp slt i32 %h, 2", but in this case the sdiv has
+; another use, so it wouldn't a big win, and it would also
+; obfuscate an otherise obvious smax pattern to the point where
+; other analyses wouldn't recognize it.
+
+define i32 @foo(i32 %h) {
+  %sd = sdiv i32 %h, 2
+  %t = icmp slt i32 %sd, 1
+  %r = select i1 %t, i32 %sd, i32 1
+  ret i32 %r
+}
+
+define i32 @bar(i32 %h) {
+  %sd = sdiv i32 %h, 2
+  %t = icmp sgt i32 %sd, 1
+  %r = select i1 %t, i32 %sd, i32 1
+  ret i32 %r
+}
+