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[ARM] Lower unsigned saturation to USAT
Summary: Implement lower of unsigned saturation on an interval [0, k] where k + 1 is a power of two using USAT instruction in a similar way to how [~k, k] is lowered using SSAT on ARM models that supports it. Patch by Marten Svanfeldt Reviewers: t.p.northover, pbarrio, eastig, SjoerdMeijer, javed.absar, fhahn Reviewed By: fhahn Subscribers: fhahn, aemerson, javed.absar, llvm-commits, kristof.beyls Differential Revision: https://reviews.llvm.org/D41348 llvm-svn: 321164
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; RUN: llc -mtriple=armv4t-eabi %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=V4T | ||
; RUN: llc -mtriple=armv6-eabi %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=V6 | ||
; RUN: llc -mtriple=armv6t2-eabi %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=V6T2 | ||
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; Check for several conditions that should result in USAT. | ||
; For example, the base test is equivalent to | ||
; x < 0 ? 0 : (x > k ? k : x) in C. All patterns that bound x | ||
; to the interval [0, k] where k + 1 is a power of 2 can be | ||
; transformed into USAT. At the end there are some tests | ||
; checking that conditionals are not transformed if they don't | ||
; match the right pattern. | ||
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; | ||
; Base tests with different bit widths | ||
; | ||
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; x < 0 ? 0 : (x > k ? k : x) | ||
; 32-bit base test | ||
define i32 @unsigned_sat_base_32bit(i32 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_base_32bit: | ||
; V6: usat r0, #23, r0 | ||
; V6T2: usat r0, #23, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %x | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %saturateUp | ||
ret i32 %saturateLow | ||
} | ||
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; x < 0 ? 0 : (x > k ? k : x) | ||
; 16-bit base test | ||
define i16 @unsigned_sat_base_16bit(i16 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_base_16bit: | ||
; V6: usat r0, #11, r0 | ||
; V6T2: usat r0, #11, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpLow = icmp slt i16 %x, 0 | ||
%cmpUp = icmp sgt i16 %x, 2047 | ||
%saturateUp = select i1 %cmpUp, i16 2047, i16 %x | ||
%saturateLow = select i1 %cmpLow, i16 0, i16 %saturateUp | ||
ret i16 %saturateLow | ||
} | ||
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; x < 0 ? 0 : (x > k ? k : x) | ||
; 8-bit base test | ||
define i8 @unsigned_sat_base_8bit(i8 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_base_8bit: | ||
; V6: usat r0, #5, r0 | ||
; V6T2: usat r0, #5, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpLow = icmp slt i8 %x, 0 | ||
%cmpUp = icmp sgt i8 %x, 31 | ||
%saturateUp = select i1 %cmpUp, i8 31, i8 %x | ||
%saturateLow = select i1 %cmpLow, i8 0, i8 %saturateUp | ||
ret i8 %saturateLow | ||
} | ||
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; | ||
; Tests where the conditionals that check for upper and lower bounds, | ||
; or the < and > operators, are arranged in different ways. Only some | ||
; of the possible combinations that lead to USAT are tested. | ||
; | ||
; x < 0 ? 0 : (x < k ? x : k) | ||
define i32 @unsigned_sat_lower_upper_1(i32 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_lower_upper_1: | ||
; V6: usat r0, #23, r0 | ||
; V6T2: usat r0, #23, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%cmpUp = icmp slt i32 %x, 8388607 | ||
%saturateUp = select i1 %cmpUp, i32 %x, i32 8388607 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %saturateUp | ||
ret i32 %saturateLow | ||
} | ||
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; x > 0 ? (x > k ? k : x) : 0 | ||
define i32 @unsigned_sat_lower_upper_2(i32 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_lower_upper_2: | ||
; V6: usat r0, #23, r0 | ||
; V6T2: usat r0, #23, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpLow = icmp sgt i32 %x, 0 | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %x | ||
%saturateLow = select i1 %cmpLow, i32 %saturateUp, i32 0 | ||
ret i32 %saturateLow | ||
} | ||
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; x < k ? (x < 0 ? 0 : x) : k | ||
define i32 @unsigned_sat_upper_lower_1(i32 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_upper_lower_1: | ||
; V6: usat r0, #23, r0 | ||
; V6T2: usat r0, #23, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpUp = icmp slt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 %saturateLow, i32 8388607 | ||
ret i32 %saturateUp | ||
} | ||
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; x > k ? k : (x < 0 ? 0 : x) | ||
define i32 @unsigned_sat_upper_lower_2(i32 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_upper_lower_2: | ||
; V6: usat r0, #23, r0 | ||
; V6T2: usat r0, #23, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; k < x ? k : (x > 0 ? x : 0) | ||
define i32 @unsigned_sat_upper_lower_3(i32 %x) #0 { | ||
; CHECK-LABEL: unsigned_sat_upper_lower_3: | ||
; V6: usat r0, #23, r0 | ||
; V6T2: usat r0, #23, r0 | ||
; V4T-NOT: usat | ||
entry: | ||
%cmpUp = icmp slt i32 8388607, %x | ||
%cmpLow = icmp sgt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 %x, i32 0 | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; | ||
; The following tests check for patterns that should not transform | ||
; into USAT but are similar enough that could confuse the selector. | ||
; | ||
; x > k ? k : (x > 0 ? 0 : x) | ||
; First condition upper-saturates, second doesn't lower-saturate. | ||
define i32 @no_unsigned_sat_missing_lower(i32 %x) #0 { | ||
; CHECK-LABEL: no_unsigned_sat_missing_lower | ||
; CHECK-NOT: usat | ||
entry: | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%cmpLow = icmp sgt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; x < k ? k : (x < 0 ? 0 : x) | ||
; Second condition lower-saturates, first doesn't upper-saturate. | ||
define i32 @no_unsigned_sat_missing_upper(i32 %x) #0 { | ||
; CHECK-LABEL: no_unsigned_sat_missing_upper: | ||
; CHECK-NOT: usat | ||
entry: | ||
%cmpUp = icmp slt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; Lower constant is different in the select and in the compare | ||
define i32 @no_unsigned_sat_incorrect_constant(i32 %x) #0 { | ||
; CHECK-LABEL: no_unsigned_sat_incorrect_constant: | ||
; CHECK-NOT: usat | ||
entry: | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 -1, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; The interval is not [0, k] | ||
define i32 @no_unsigned_sat_incorrect_interval(i32 %x) #0 { | ||
; CHECK-LABEL: no_unsigned_sat_incorrect_interval: | ||
; CHECK-NOT: usat | ||
entry: | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %x, -4 | ||
%saturateLow = select i1 %cmpLow, i32 -4, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; The returned value (y) is not the same as the tested value (x). | ||
define i32 @no_unsigned_sat_incorrect_return(i32 %x, i32 %y) #0 { | ||
; CHECK-LABEL: no_unsigned_sat_incorrect_return: | ||
; CHECK-NOT: usat | ||
entry: | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %x, 0 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %y | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} | ||
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; One of the values in a compare (y) is not the same as the rest | ||
; of the compare and select values (x). | ||
define i32 @no_unsigned_sat_incorrect_compare(i32 %x, i32 %y) #0 { | ||
; CHECK-LABEL: no_unsigned_sat_incorrect_compare: | ||
; CHECK-NOT: usat | ||
entry: | ||
%cmpUp = icmp sgt i32 %x, 8388607 | ||
%cmpLow = icmp slt i32 %y, 0 | ||
%saturateLow = select i1 %cmpLow, i32 0, i32 %x | ||
%saturateUp = select i1 %cmpUp, i32 8388607, i32 %saturateLow | ||
ret i32 %saturateUp | ||
} |